View source for Engineering:M16 rifle

{{Short description|American assault rifle}}
{{Infobox weapon
| name               = M16
| image              = File:M16A2 noBG.jpg
| image_size         = 300
| caption            = M16A2, multi-sided view
| origin             = United States <!-- WP:INFOBOXFLAG -->
| type               = [[Engineering:Assault rifle|Assault rifle]]
<!-- Type selection -->
| is_ranged          = Yes
<!-- Service history -->
| service            = 1964–present{{Sfn|Rottman|2011|p=74}}
| wars               = See ''Conflicts''
| used_by            = See ''Users''
<!-- Production history -->
| designer           = Eugene Stoner (AR-10)<ref>{{cite web| url = https://www.americanrifleman.org/articles/2018/10/2/the-ar-10-story/| title = The AR-10 Story {{!}} An Official Journal Of The NRA}}</ref> <br />L. James Sullivan (AR-15)<ref>{{cite web| url = https://www.washingtontimes.com/news/2016/may/31/jim-sullivan-ar-15-designer-accuses-hbo-of-decepti/| title = Jim Sullivan, AR-15 designer, accuses HBO of deceptively editing interview - Washington Times| website = The Washington Times}}</ref><!-- <ref>{{Cite journal |title=Focus on Basics, Urges Small Arms Designer |first=Virginia Hart |last=Ezell |date=November 2001 |journal=National Defense |url=http://www.nationaldefensemagazine.org/archive/2001/November/Pages/Focus_on4174.aspx|url-status=dead |archive-url= https://web.archive.org/web/20101207022745/http://www.nationaldefensemagazine.org/ARCHIVE/2001/NOVEMBER/Pages/Focus_on4174.aspx |archive-date=7 December 2010}}</ref> -->
| manufacturer       = {{Plainlist|
* Colt's Manufacturing Company
* Daewoo Precision Industries
* FN Herstal
* Harrington & Richardson
* [[Company:General Motors|General Motors]] [[Engineering:Hydramatic|Hydramatic]] Division
* Elisco
* U.S. Ordnance
}}
| unit_cost          = 
| production_date    = {{plainlist|
* 1963–present{{Sfn|Rottman|2011|p=74}}}}
| number             = c. 8 million as of 2011{{Sfn|Rottman|2011|p=74}}
| variants           = See ''List of Colt AR-15 and M16 rifle variants''
<!-- General specifications -->
| spec_label         = M16
| weight             = unloaded: <br />{{convert|6.37|lb|kg|2|abbr=on}} (M16A1) <br />{{convert|7.5|lb|kg|2|abbr=on}} (without magazine and sling) (M16A2)<ref name="ReferenceB">{{Cite web|url=http://archive.org/details/a2-m4-m4a1-technical|title=US Army M16A2, M4, and M4A1 Technical Manual|date=4 May 1991|via=Internet Archive}}</ref> <br />{{convert|7.5|lb|kg|2|abbr=on}} (M16A4) <br />{{convert|8.81|lb|kg|2|abbr=on}} (loaded with 30 rounds and sling)<ref name="McNab 2021 13">{{Cite book|last=McNab|first=Chris|title=The M4 Carbine|publisher=Osprey Publishing|year=2021|pages=13}}</ref><ref name="ReferenceB">{{Cite web|url=http://archive.org/details/a2-m4-m4a1-technical|title=US Army M16A2, M4, and M4A1 Technical Manual|date=4 May 1991|via=Internet Archive}}</ref>
| length             = {{convert|38.81|in|mm|0|abbr=on}} (M16A1) <br />{{convert|39.63|in|mm|0|abbr=on}} (M16A2) <br />{{convert|39.37|in|mm|0|abbr=on}} (M16A4)
| part_length        = {{convert|20|in|mm|0|abbr=on}}
<!-- Ranged weapon specifications -->
| cartridge          = [[Engineering:5.56×45mm NATO|5.56×45&nbsp;mm NATO]]
| caliber            = 5.56&nbsp;mm (.223&nbsp;in)
| action             = [[Engineering:Gas-operated reloading|Gas-operated]] (Expansion of gas within piston inside bolt carrier), [[Engineering:Closed bolt|closed]] [[Engineering:Rotating bolt|rotating bolt]]
| rate               = 700–800 rounds/min cyclic sustained (M16A1)<ref name=Rottman26>{{harvnb|Rottman|2011|p=26}}</ref> <br />700-900 rounds/min cyclic sustained (M16A2, M16A3)<ref name="Rottman40">{{harvnb|Rottman|2011|p=40}}</ref> <br />800 rounds/min cyclic sustained (M16A4)<ref name="Rottman40"/>
| velocity           = {{convert|3150|ft/s|m/s|0|abbr=on}} ([[Engineering:5.56×45mm NATO#M855A1|M855A1]] round)<ref>{{cite web|url=https://acc.dau.mil/adl/en-US/382846/file/68848/Public%20Release%20EPR%20Apr12.pdf|title=M855A1 Enhanced Performance Round (EPR), LTC Philip Clark, Product Manager Small Caliber Ammunition, April 2012|publisher=Acc.dau.mil|access-date=25 February 2017|archive-url=https://web.archive.org/web/20170125120308/https://acc.dau.mil/adl/en-US/382846/file/68848/Public%20Release%20EPR%20Apr12.pdf|archive-date=25 January 2017|url-status=dead}}</ref>
| range              = {{convert|550|m|yd|0|abbr=on}} (point target)<ref>{{cite web |url=http://www.peosoldier.army.mil/portfolio/#202 |title=M16A2/A4 rifle |publisher=peosoldier.army.mil |access-date=29 July 2015 |archive-url=https://web.archive.org/web/20140724043400/http://www.peosoldier.army.mil/portfolio/#202 |archive-date=24 July 2014 |url-status=dead}}</ref> <br />{{convert|800|m|yd|0|abbr=on}} (area target)<ref>{{cite web |url=http://www.armystudyguide.com/content/army_board_study_guide_topics/m16a2/m16a2-study-guide.shtml |title=M16/A2 – 5.56 mm Semiautomatic Rifle |publisher=ArmyStudyGuide.com |access-date=13 July 2014 |archive-url=https://web.archive.org/web/20140706211034/http://www.armystudyguide.com/content/army_board_study_guide_topics/m16a2/m16a2-study-guide.shtml |archive-date=6 July 2014 |url-status=live}}</ref>
| max_range          = {{convert|3600|m|yd|0|abbr=on}}
| feed               = [[Engineering:STANAG magazine|STANAG magazine]] <br />20-round detachable box magazine: <br />{{convert|0.211|lb|kg|abbr=on}} (empty) / {{convert|0.738|lb|kg|abbr=on}} (full) <br />30-round detachable box magazine: <br />{{convert|0.257|lb|kg|abbr=on}} (empty) / {{convert|1.06|lb|kg|abbr=on}} (full) <br />60-round detachable box magazine <br />[[Engineering:Beta C-Mag|Beta C-Mag]] 100-round [[Engineering:Drum magazine|drum magazine]]: <br />{{convert|2.2|lb|kg|abbr=on}} (empty) / {{convert|4.81|lb|kg|abbr=on}} (full)
| sights             = [[Engineering:Iron sights|Iron sights]]: <br />Rear: aperture; L-type flip <br />Front: wing-protected post <br />Various aiming optics
}}

The '''M16 rifle''' (officially designated '''Rifle, Caliber 5.56&nbsp;mm, M16''') is a family of [[Engineering:Service rifle|military rifles]] adapted from the [[Engineering:ArmaLite AR-15|ArmaLite AR-15]]<!-- Do NOT change: the ArmaLite AR-15 is not the same weapon as the Colt AR-15, in spite of the name... --> rifle for the United States military. The original M16 rifle was a [[Engineering:5.56×45mm NATO|5.56×45mm]] [[Engineering:Automatic rifle|automatic rifle]] with a 20-round magazine.

In 1964, the M16 entered US military service and the following year was deployed for [[Social:Jungle warfare|jungle warfare]] operations during the Vietnam War.<ref name="autogenerated5" /> In 1969, the M16A1 replaced the M14 rifle to become the US military's standard service rifle.<ref name="SAOW"/><ref name="Urdang, p. 801">Urdang, p. 801.</ref> The M16A1 incorporated numerous modifications including a bolt-assist, chrome-plated bore, protective reinforcement around the magazine release, and revised flash hider.<ref name="autogenerated5" />

In 1983, the US Marine Corps adopted the M16A2 rifle, and the US Army adopted it in 1986. The M16A2 fires the improved 5.56×45mm (M855/SS109) cartridge and has a newer adjustable rear sight, case deflector, heavy barrel, improved [[Engineering:Handguard|handguard]], pistol grip, and buttstock, as well as a semi-auto and three-round burst fire selector.<ref>{{cite web |url=http://apps.dtic.mil/dtic/tr/fulltext/u2/a168577.pdf |title=ARI Research Note 86-19, ANALYSIS OF M16A2 RIFLE CHARACTERISTICS AND RECOMMENDED IMPROVEMENTS |archive-url=https://web.archive.org/web/20170329041706/http://www.dtic.mil/dtic/tr/fulltext/u2/a168577.pdf |archive-date=29 March 2017 |author1=Osborne, Arthur D. |website=Mellonics Systems Development Division, Litton Systems, Inc|author2= Smith, Seward|location=Fort Benning, Georgia |publisher=ARI Field Unit, Training Research Laboratory, United States Army – Research Institute for the Behavioral and Social Sciences |url-status=live |date=February 1986}}</ref><ref>Venola p. 6-18</ref> Adopted in July 1997, the M16A4 is the fourth generation of the M16 series. It is equipped with a removable carrying handle and [[Engineering:Picatinny rail|Picatinny rail]] for mounting optics and other ancillary devices.<ref name="Modern Marines 2004, page 16">{{cite book |title=Weapons of the Modern Marines|author1=Green, Michael|publisher=MBI Publishing Company|url=https://www.amazon.com/Weapons-Marines-Battlegear-Michael-2004-03-13/dp/B01K3N75CE |date=13 March 2004 |page=16|isbn=978-0-7603-1697-9 }}</ref>

The M16 has also been widely adopted by other armed forces around the world. Total worldwide production of M16s is approximately 8 million, making it the most-produced firearm of its 5.56&nbsp;mm caliber.<ref name="Colt_Weapon_Systems">{{cite web|url=http://www.colt.com/mil/M16.asp |title=M16 5.56mm Rifle|date=2 June 2003|website=Colt.com |url-status=dead|archive-url=https://web.archive.org/web/20030602074644/http://www.colt.com/mil/M16.asp|archive-date=2 June 2003}}</ref>{{Sfn|Rottman|2011|p=74}} The US military has largely replaced the M16 in frontline combat units with a shorter and lighter version, the [[Engineering:M4 carbine|M4 carbine]].<ref name=Small_Arms_Individual>{{cite web |title=Small Arms–Individual Weapons |url=https://fas.org/man/dod-101/sys/land/wsh2011/290.pdf |access-date=8 November 2010 |date=3 November 2010 |archive-url=https://web.archive.org/web/20110209114148/http://www.fas.org/man/dod-101/sys/land/wsh2011/290.pdf |archive-date=9 February 2011 |url-status=live}}</ref><ref name="militarytimes26oct15" />

In April 2022, the U.S. Army selected the [[Engineering:SIG MCX|SIG MCX SPEAR]] as the winner of the Next Generation Squad Weapon Program to replace the M16/M4. The rifle is designated XM7.<ref>[https://www.armytimes.com/news/your-army/2022/04/19/army-chooses-sig-sauer-to-build-its-next-generation-squad-weapon/ "Army chooses Sig Sauer to build its Next Generation Squad Weapon"]. ''Army Times''. 19 April 2022.</ref>

==History==
===Background===
<!-- This section is linked from [[Engineering:Assault rifle|Assault rifle]] -->
In 1928, a U.S. Army 'Caliber Board' conducted firing tests at Aberdeen Proving Ground and recommended transitioning to smaller caliber rounds, mentioning, in particular {{cvt|.27|in|mm|sigfig=3}} caliber. Largely in deference to tradition, this recommendation was ignored and the Army referred to the {{cvt|.30|in|mm|sigfig=3}} caliber as "full-sized" for the next 35 years.<ref name="Atlantic_Fallows">{{cite news |last1=Fallows |first1=James |title=M-16: A Bureaucratic Horror Story |url=https://www.theatlantic.com/magazine/archive/1981/06/m-16-a-bureaucratic-horror-story/545153/ |access-date=1 April 2019 |work=The Atlantic |date=1 June 1981 |archive-url=https://web.archive.org/web/20190401042658/https://www.theatlantic.com/magazine/archive/1981/06/m-16-a-bureaucratic-horror-story/545153/ |archive-date=1 April 2019 |url-status=live}}</ref> After World War II, the United States military started looking for a single automatic rifle to replace the M1 Garand, [[Engineering:M1 carbine|M1/M2 Carbines]], [[Engineering:M1918 Browning Automatic Rifle|M1918 Browning Automatic Rifle]], [[Engineering:M3 submachine gun|M3 "Grease Gun"]] and [[Engineering:Thompson submachine gun|Thompson submachine gun]].<ref name="ReferenceA" />{{Sfn|Rottman|2011|p=6}} However, early experiments with select-fire versions of the M1 Garand proved disappointing.<ref>{{cite web |url=http://www.nramuseum.com/media/940585/m14.pdf |title=Cut down in its Youth, Arguably Americas Best Service Rifle, the M14 Never Had the Chance to Prove Itself |first=Philip |last=Schreier |date=September 2001 |pages=24–29, 46 |publisher=NRA Museum |access-date=3 June 2019 |archive-url=https://web.archive.org/web/20131204025725/http://www.nramuseum.com/media/940585/m14.pdf |archive-date=4 December 2013 |url-status=dead}}</ref> During the Korean War, the select-fire M2 carbine largely replaced the [[Engineering:Submachine gun|submachine gun]] in US service{{Sfn|Rottman|2011|p=6}} and became the most widely used carbine variant.<ref>{{cite book |first=Leroy |last=Thompson |year=2011 |title=The M1 Carbine |publisher=Osprey |page=35 |isbn=978-1-84908-907-4}}</ref> However, combat experience suggested that the .30 Carbine round was underpowered.<ref>{{cite magazine |url=http://www.americanrifleman.org/articles/arms-chosin-few/|title=Arms of the Chosin Few |archive-url=https://web.archive.org/web/20131205205918/http://www.americanrifleman.org/articles/arms-chosin-few |archive-date=5 December 2013 |magazine=American Rifleman |access-date=23 November 2011}}</ref> American weapons designers concluded that an intermediate round was necessary, and recommended a small-caliber, high-velocity cartridge.<ref>{{cite web |author1=Hall, Donald L.|url=http://www.dtic.mil/dtic/tr/fulltext/u2/377335.pdf |title=An effectiveness study of the infantry rifle|archive-url=https://web.archive.org/web/20150924051902/http://www.dtic.mil/dtic/tr/fulltext/u2/377335.pdf |archive-date=24 September 2015 |format=PDF, Report No. 593|website=Ballistic Research Laboratories|location=Maryland|date= March 1952|url-status=dead|publisher=Released 29 March 1973}}</ref>

However, senior American commanders, having faced fanatical enemies and experienced major logistical problems during World War II and the Korean War,<ref>''Fanaticism and Conflict in the Modern Age'', by Matthew Hughes & Gaynor Johnson, Frank Cass & Co, 2005</ref><ref>{{cite web|url=http://www.pacificwar.org.au/JapWarCrimes/Explaining_JapWarCrimes.html|title=An Attempt To Explain Japanese War Crimes|publisher=Pacificwar.org.au|access-date=23 August 2012|archive-url=https://web.archive.org/web/20120707093008/http://www.pacificwar.org.au/JapWarCrimes/Explaining_JapWarCrimes.html|archive-date=7 July 2012|url-status=live}}</ref><ref>{{cite web|url=http://www.history.army.mil/books/korea/20-2-1/toc.htm|title=South to the Naktong – North to the Yalu|publisher=History.army.mil|access-date=23 August 2012|archive-url=https://web.archive.org/web/20140207235336/http://www.history.army.mil/books/korea/20-2-1/toc.htm|archive-date=7 February 2014|url-status=live}}</ref><ref>{{cite web|url=http://www.ibiblio.org/hyperwar/USA/BigL/index.html#contents|title=HyperWar: The Big 'L'-American Logistics in World War II|publisher=Ibiblio.org|access-date=24 December 2011|archive-url=https://web.archive.org/web/20131203004311/http://www.ibiblio.org/hyperwar/USA/BigL/index.html#contents|archive-date=3 December 2013|url-status=live}}</ref><ref>{{cite web|url=http://www.almc.army.mil/alog/issues/NovDec03/Logistics_of_Invasion.htm |title=The Logistics of Invasion|website=Almc.army.mil|access-date=23 November 2011|url-status=dead|archive-url=https://web.archive.org/web/20150622011454/http://www.almc.army.mil/alog/issues/NovDec03/Logistics_of_Invasion.htm|archive-date=22 June 2015}}</ref> insisted that a single, powerful .30 caliber cartridge be developed, that could not only be used by the new automatic rifle but by the new [[Engineering:General-purpose machine gun|general-purpose machine gun]] (GPMG) in concurrent development.<ref name="independencearmory1">{{cite web|first=E. H. (Col.)|last=Harrison (NRA Technical Staff)|url=http://independencearmory.com/downloads/M14_Articles/American%20Rifleman%20-%20New%20Service%20Rifle_%20Amer.%20Rifleman%20June,%201957.pdf |title=New Service Rifle|date=June 1957|url-status=dead|archive-url=https://web.archive.org/web/20151107045353/http://independencearmory.com/downloads/M14_Articles/American%20Rifleman%20-%20New%20Service%20Rifle_%20Amer.%20Rifleman%20June%2C%201957.pdf|archive-date=7 November 2015}}</ref><ref>{{cite web|first=Anthony G.|last=Williams|url=http://www.quarry.nildram.co.uk/Assault.htm |title=Assault Rifles And Their Ammunition: History and Prospects|archive-url=https://web.archive.org/web/20140602021550/http://www.quarry.nildram.co.uk/Assault.htm|archive-date=2 June 2014|website=Quarry.nildram.co.uk|date=3 February 2012|access-date=23 November 2011}}</ref> This culminated in the development of the [[Engineering:7.62×51mm NATO|7.62×51&nbsp;mm NATO]] cartridge.<ref name="independencearmory1" />

The U.S. Army then began testing several rifles to replace the obsolete M1. Springfield Armory's T44E4 and heavier T44E5 were essentially updated versions of the M1 chambered for the new 7.62&nbsp;mm round, while Fabrique Nationale submitted their FN FAL as the T48. ArmaLite entered the competition late, hurriedly submitting several AR-10 prototype rifles in the fall of 1956 to the U.S. Army's Springfield Armory for testing.<ref name="Pikula36, 38">Pikula, pp. 36, 38</ref> The AR-10 featured an innovative straight-line barrel/stock design, forged aluminum alloy receivers, and with [[Chemistry:Phenol formaldehyde resin#Applications|phenolic composite]] stocks.<ref name="Pikula, Sam pp. 27-29">Pikula, Major Sam. ''The ArmaLite AR-10''. Regnum Fund Press, 1998. {{ISBN|9986-494-38-9}}. pp. 27-29</ref> It had rugged elevated sights, an oversized aluminum<ref>Pikula, Sam (Major), ''The ArmaLite AR-10'', p. 38: Later changed to titanium.</ref> [[Engineering:Flash suppressor|flash suppressor]] and [[Engineering:Muzzle brake|recoil compensator]], and an adjustable gas system.<ref name="Pikula27-30">Pikula, pp. 27-30</ref> The final prototype featured an upper and lower receiver with the now-familiar hinge and takedown pins, and the charging handle was on top of the receiver placed inside of the carry handle.<ref name="Pikula36, 38" /> For a 7.62&nbsp;mm NATO rifle, the AR-10 was incredibly lightweight at only {{cvt|6.85|lb|kg}} empty.<ref name="Pikula36, 38" /> Initial comments by Springfield Armory test staff were favorable, and some testers commented that the AR-10 was the best lightweight automatic rifle ever tested by the Armory.<ref>{{cite journal|last=Lewis|first=Jack|title=The M-14: Boon or Blunder|journal=Gun World|year=1963|volume=3|issue=4}}</ref><ref name="Pikula39-40">Pikula, pp. 39-40</ref> In the end, the U.S. Army chose the T44, now named the M14 rifle,<ref name="independencearmory1" /> which was an improved M1 Garand with a 20-round magazine and automatic fire capability.<ref name="smallarmsreview.com">{{cite journal|url=http://www.smallarmsreview.com/display.article.cfm?idarticles=2434|journal=Small Arms Review|volume=5|issue=7|title=M14 vs. M16 in Vietnam|first=Robert|last=Bruce|date=April 2002|access-date=3 June 2019|archive-url=https://web.archive.org/web/20160422004206/http://www.smallarmsreview.com/display.article.cfm?idarticles=2434|archive-date=22 April 2016|url-status=live}}</ref><ref>{{cite journal|journal=Jane's International Defense Review|volume=36|year=2003|page=43|quote=The M14 is basically an improved M1 with a modified gas system and detachable 20-round magazine. |title=The M14}}</ref> The U.S. also adopted the [[Engineering:M60 machine gun|M60]] general-purpose machine gun (GPMG).<ref name="independencearmory1" /> Its NATO partners adopted the FN FAL and HK G3 rifles, as well as the [[Engineering:FN MAG|FN MAG]] and Rheinmetall MG3 GPMGs.

The first confrontations between the [[Engineering:AK-47|AK-47]] and the M14 came in the early part of the Vietnam War. Battlefield reports indicated that the M14 was uncontrollable in full-auto and that soldiers could not carry enough ammunition to maintain fire superiority over the AK-47.<ref name="smallarmsreview.com" /><ref>{{Citation |first= Lee |last= Emerson |date= 10 October 2006 |title= M14 Rifle History and Development |url= http://www.imageseek.com/m1a/M14_RHAD_Online_Edition_061010.pdf |access-date= 3 June 2019 |archive-url= https://web.archive.org/web/20171215062553/http://www.imageseek.com/m1a/M14_RHAD_Online_Edition_061010.pdf |archive-date= 15 December 2017 |url-status= dead}}</ref> And, while the M2 carbine offered a high rate of fire, it was under-powered and ultimately outclassed by the AK-47.{{Sfn|Rottman|2011|p=41}} A replacement was needed: a medium between the traditional preference for high-powered rifles such as the M14, and the lightweight firepower of the M2 Carbine.{{citation needed|date=April 2019}}

As a result, the Army was forced to reconsider a 1957 request by General Willard G. Wyman, commander of the U.S. Continental Army Command (CONARC) to develop a .223-inch caliber (5.56&nbsp;mm) select-fire rifle weighing {{convert|6|lb|kg|abbr= on}} when loaded with a 20-round magazine.<ref name="ReferenceA">{{cite web |author1=Ehrhart, Major Thomas P. |url=https://apps.dtic.mil/sti/pdfs/ADA512331.pdf |title=Increasing Small Arms Lethality in Afghanistan: Taking Back the Infantry Half-Kilometer|archive-url=https://web.archive.org/web/20130719043744/http://www.dtic.mil/cgi-bin/GetTRDoc?AD=ADA512331&Location=U2&doc=GetTRDoc.pdf |archive-date=19 July 2013 |website=U.S. Army|url-status=live |date=2009}}</ref> The 5.56&nbsp;mm round had to penetrate a standard U.S. helmet at {{convert|500|yd|m|abbr=off|sp=us}} and retain a velocity over the speed of sound while matching or exceeding the wounding ability of the .30 Carbine cartridge.<ref name="Hutton, Robert 1971">{{cite book |author1=Hutton, Robert |title=The .223 |publisher=Guns & Ammo Annual ed|date=1971}}</ref>

This request ultimately resulted in the development of a scaled-down version of the Armalite AR-10, named the [[Engineering:ArmaLite AR-15|ArmaLite AR-15]].<ref name="m-14parts.com">{{ cite web |author1=Kern, Danford Allan |date=2006|url=http://www.m-14parts.com/M14toM16.pdf |title=The influence of organizational culture on the acquisition of the m16 rifle|archive-url=https://web.archive.org/web/20131105215841/http://www.m-14parts.com/M14toM16.pdf |archive-date=5 November 2013|website=m-14parts.com |publisher=A thesis presented to the Faculty of the US Army Command and General Staff College in partial fulfillment of the requirements for the degree MASTER OF MILITARY ART AND SCIENCE, Military History |location=Fort Leavenworth, Kansas}}</ref><ref name="nodakspud.com">{{cite web|author1=Kokalis, Peter G. |url=http://www.nodakspud.com/RetroAR15.pdf|title=Retro AR-15|archive-url=https://web.archive.org/web/20131029202308/http://www.nodakspud.com/RetroAR15.pdf |archive-date=29 October 2013 |website=Nodakspud.com}}</ref><ref name="SAOW"/> The AR-15 was first revealed by Eugene Stoner at Fort Benning in May 1957.{{Sfn|Rottman|2011|p=8}} The AR-15 used .22-caliber bullets, which destabilized when they hit a human body, as opposed to the .30 round, which typically passed through in a straight line. The smaller caliber meant that it could be controlled in autofire due to the reduced [[Engineering:Bolt thrust|bolt thrust]] and [[Engineering:Free recoil|free recoil]] impulse. Being almost one-third the weight of the .30 meant that the soldier could sustain fire for longer with the same load. Due to design innovations, the AR-15 could fire 600 to 700 rounds a minute with an extremely low jamming rate. Parts were stamped out, not hand-machined, so they could be mass-produced, and the stock was plastic to reduce weight.<ref name="Atlantic_Fallows"/>

In 1958, the Army's Combat Developments Experimentation Command ran experiments with small squads in combat situations using the M14, AR-15, and another rifle designed by Winchester. The resulting study recommended adopting a lightweight rifle like the AR-15. In response, the Army declared that all rifles and machine guns should use the same ammunition and ordered full production of the M14.<ref name="Atlantic_Fallows"/> However, advocates for the AR-15 gained the attention of Air Force Chief of Staff General Curtis LeMay. After testing the AR-15 with the ammunition manufactured by Remington that Armalite and Colt recommended, the Air Force declared that the AR-15 was its 'standard model' and ordered 8,500 rifles and 8.5 million rounds.<ref name="Atlantic_Fallows"/> Advocates for the AR-15 in the Defense Advanced Research Projects Agency acquired 1,000 Air Force AR-15s and shipped them to be tested by the Army of the Republic of Vietnam (ARVN). The South Vietnam soldiers issued glowing reports of the weapon's reliability, recording zero broken parts while firing 80,000 rounds in one stage of testing, and requiring only two replacement parts for the 1,000 weapons over the entire course of testing. The report of the experiment recommended that the U.S. provide the AR-15 as the standard rifle of the ARVN, but Admiral Harry Felt, then Commander in Chief of Pacific Forces, rejected the recommendations on the advice of the U.S. Army.<ref name="Atlantic_Fallows"/>

Throughout 1962 and 1963, the U.S. military extensively tested the AR-15. Positive evaluations emphasized its lightness, "lethality", and reliability.<ref name="Atlantic_Fallows"/> However, the Army Materiel Command criticized its inaccuracy at longer ranges and lack of penetrating power at higher ranges.<ref name="m-14parts.com" /><ref name="smallarmsreview.com" /><ref name="Atlantic_Fallows"/> In early 1963, the U.S. Special Forces asked and was given permission, to make the AR-15 its standard weapon. Other users included Army Airborne units in Vietnam and some units affiliated with the Central Intelligence Agency. As more units adopted the AR-15, Secretary of the Army Cyrus Vance ordered an investigation into why the weapon had been rejected by the Army. The resulting report found that Army Materiel Command had rigged the previous tests, selecting tests that would favor the M14 and choosing [[Engineering:Match grade|match grade]] M14s to compete against AR-15s out of the box.<ref name="Atlantic_Fallows"/> At this point, the bureaucratic battle lines were well-defined, with the Army ordnance agencies opposed to the AR-15 and the Air Force and civilian leadership of the Defense Department in favor.<ref name="Atlantic_Fallows"/>

In January 1963, Secretary of Defense Robert McNamara concluded that the AR-15 was the superior weapon system and ordered a halt to M14 production.<ref name="m-14parts.com" /><ref name="smallarmsreview.com" /> In late 1963, the Defense Department began mass procurement of rifles for the Air Force and special Army units. Secretary McNamara designated the Army as the procurer for the weapon with the Department, which allowed the Army ordnance establishment to modify the weapon as they wished. The first modification was the addition of a "manual bolt closure," allowing a soldier to ram in a round if it failed to seat properly. The Air Force, which was buying the rifle, and the Marine Corps, which had tested it both objected to this addition, with the Air Force noting, "During three years of testing and operation of the AR-15 rifle under all types of conditions the Air Force has no record of malfunctions that could have been corrected by a manual bolt closing device." They also noted that the closure added weight and complexity, reducing the reliability of the weapon. Colonel Harold Yount, who managed the Army procurement, would later state the bolt closure was added after direction from senior leadership, rather than as a result of any complaint or test result, and testified about the reasons: "the M-1, the M-14, and the carbine had always had something for the soldier to push on; that maybe this would be a comforting feeling to him or something."<ref name="Atlantic_Fallows"/><ref>{{cite book |title=Hearings before the Special Subcommittee on the M-16 Rifle Program of the Committee on Armed Services, House of Representatives, Ninetieth Congress, first session, 15 May, 16, 31, 21 June, 25 July, 26, 27, 8 August, 9, and 22, 1967. |year = 1967|url=https://hdl.handle.net/2027/uiug.30112109164266?urlappend=%3Bseq=121 |publisher=U.S. House of Representatives |access-date=1 April 2019 |page=4545|hdl= 2027/uiug.30112109164266?urlappend=%3Bseq=121}}</ref>

After modifications,<ref name="nodakspud.com" /> the new redesigned rifle was subsequently adopted as the M16 Rifle:<ref name="autogenerated5" /><ref name="m-14parts.com" /><ref name="smallarmsreview.com" />
{{blockquote|(The M16) was much lighter compared to the M14 it replaced, ultimately allowing soldiers to carry more ammunition. The air-cooled, gas-operated, magazine-fed assault rifle was made of steel, aluminum alloy, and composite plastics, truly cutting-edge for the time. Designed with full and semi-automatic capabilities, the weapon initially did not respond well to wet and dirty conditions, sometimes even jamming in combat. After a few minor modifications, the weapon gained in popularity among troops on the battlefield.<ref name="smallarmsreview.com" /><ref>GX. The Guard Experience. The Pride of the Guard. by Major Darrin Haas. Volume 10. Issue 3. 2013. Page 67. "Nicknamed a 'Mattel toy' because of its small caliber and lightweight design, the M16 became the standard service rifle for U.S. forces in Vietnam in 1967. The weapon was much lighter compared to the M14 it replaced, ultimately allowing Soldiers to carry more ammunition. The air-cooled, gas-operated, magazine-fed assault rifle was made of steel, aluminum alloy and composite plastics, truly cutting-edge for the time. Designed with full and semi-automatic capabilities, the weapon initially did not respond well to wet and dirty conditions, sometimes even jamming in combat. After a few minor modifications, the weapon gained in popularity among troops on the battlefield. Still in service today, the M16 is being phased out by the M4 carbine.</ref><ref name="a953117" />}}

Despite its early failures the M16 proved to be a revolutionary design and stands as the longest continuously serving rifle in US military history.<ref name="autogenerated5" /><ref name="m-14parts.com" /> It has been adopted by many US allies and the [[Engineering:5.56×45mm NATO|5.56×45&nbsp;mm NATO]] cartridge has become not only the NATO standard but "the standard assault-rifle cartridge in much of the world."<ref name="m-14parts.com" /><ref>''Small Arms''. By Martin J. Dougherty. The Rosen Publishing Group, 15 December 2012. page 26</ref><ref name="autogenerated3">{{cite web |author1=Arvidsson, Per G. |url=http://www.dtic.mil/ndia/2009infantrysmallarms/wednesdaysessionvArvidsson.pdf |title=Weapons & Sensors |archive-url=https://web.archive.org/web/20150924131614/http://www.dtic.mil/ndia/2009infantrysmallarms/wednesdaysessionvArvidsson.pdf |archive-date=24 September 2015 |url-status=dead |website=NATO Army Armaments Group}}</ref> It also led to the development of small-caliber high-velocity service rifles by every major army in the world.<ref name="m-14parts.com" /> It is a benchmark against which other assault rifles are judged.<ref name="m-14parts.com" /><ref>{{cite web|url=http://www.vsms.org/Forum/Seite_69_tactical_stuff/120500_Sights_Accessories_Compendium.pdf |title=Special Ops & Soldier Small Arms, Sights & Accessories |access-date=27 July 2013|url-status=dead|archive-url=https://web.archive.org/web/20131203023022/http://www.vsms.org/Forum/Seite_69_tactical_stuff/120500_Sights_Accessories_Compendium.pdf|archive-date=3 December 2013|publisher=Compendium Special Operations by Armada|website=Assault Rifles |author1=Valpolini, Paolo |date=February 2012 |quote=Among western armies the M4 with its 356-mm-long barrel remains the benchmark type, although reports from the field have shown some criticism regarding its reliability in sand and dusty environments due to the direct impingement or 'gas-tube' system that tends to bring carbon blow-back into the chamber, while hot gases used to cycle the weapon generate heat problems}}</ref><ref>{{cite journal|url=http://www.ausa.org/publications/armymagazine/archive/2008/7/Documents/SA_0708.pdf|quotation="Colt literature notes that the fourth generation of the M16 "still represents the world standard by which all other weapons of this class are judged. Its combat-proven performance is verified by the fact that over eight million M16 weapon systems have been produced and placed in military service throughout the world."|title=Soldier Armed. M16A4 Rifle|author=Scott R. Gourley|journal=Army Magazine|date=July 2008|page=75|access-date=11 January 2018|archive-url=https://web.archive.org/web/20150923180252/http://www.ausa.org/publications/armymagazine/archive/2008/7/Documents/SA_0708.pdf|archive-date=23 September 2015|url-status=live}}</ref>

===Adoption===
In July 1960, General Curtis LeMay was impressed by a demonstration of the ArmaLite AR-15. In the summer of 1961, General LeMay was promoted to U.S. Air Force chief of staff and requested 80,000 AR-15s. However, General Maxwell D. Taylor, chairman of the Joint Chiefs of Staff, advised President [[Biography:John F. Kennedy|John F. Kennedy]] that having two different calibers within the military system at the same time would be problematic and the request was rejected.<ref name=Rose_p372>{{harvnb|Rose|2009|p=372}}</ref> In October 1961, William Godel, a senior man at the Advanced Research Projects Agency, sent 10 AR-15s to South Vietnam. The reception was enthusiastic, and in 1962 another 1,000 AR-15s were sent.<ref>{{harvnb|Rose|2009|pp=372–373}}</ref> United States Army Special Forces personnel filed battlefield reports lavishly praising the AR-15 and the stopping power of the 5.56&nbsp;mm cartridge, and pressed for its adoption.<ref name="smallarmsreview.com" />

The damage caused by the 5.56&nbsp;mm bullet was originally believed to be caused by "tumbling" due to the slow 1 turn in {{convert|14|in|mm|adj=on}} rifling twist rate.<ref name="smallarmsreview.com" /><ref name=Rose_p372 /> However, any pointed lead core bullet will "tumble" after penetration into flesh, because the center of gravity is towards the rear of the bullet. The large wounds observed by soldiers in Vietnam were caused by bullet fragmentation created by a combination of the bullet's velocity and construction.<ref>{{cite web |url=http://ammo.ar15.com/ammo/project/term_tighttwist.html |title=Ammo Oracle|archive-url=https://web.archive.org/web/20110707154441/http://ammo.ar15.com/ammo/project/term_tighttwist.html |archive-date=7 July 2011|website=Ammo.ar15.com|access-date=27 September 2011}}</ref> These wounds were so devastating that the photographs remained classified into the 1980s.<ref>{{harvnb|Rose|2009|p=373}}</ref>

However, despite overwhelming evidence that the AR-15 could bring more firepower to bear than the M14, the Army opposed the adoption of the new rifle.<ref name="m-14parts.com" /><ref name="smallarmsreview.com" /> U.S. Secretary of Defense Robert McNamara now had two conflicting views: the ARPA report<ref>{{cite web|url=https://assets.documentcloud.org/documents/2859676/ARPA-AR-15.pdf|title=RESEARCH & DEVELOPMENT FIELD UNIT. Advanced Research Projects Agency. REPORT OF TASK NO. 13A. TEST OF ARMALITE RIFLE. AR-15 (U)|date=31 July 1962|website=Assets.documentcloud.org|access-date=16 January 2018}}</ref> favoring the AR-15 and the Army's position favoring the M14.<ref name="smallarmsreview.com" /> Even President Kennedy expressed concern, so McNamara ordered Secretary of the Army, Cyrus Vance, to test the M14, the AR-15, and the AK-47. The Army reported that only the M14 was suitable for service, but Vance wondered about the impartiality of those conducting the tests. He ordered the Army Inspector General to investigate the testing methods used; the inspector general confirmed that the testers were biased toward the M14.

[[File:M16a1m16a2m4m16a45wi.jpg|thumb|From top to bottom: M16A1, M16A2, M4A1, M16A4 ]]
In January 1963, Secretary McNamara received reports that M14 production was insufficient to meet the needs of the armed forces and ordered a halt to M14 production.<ref name="smallarmsreview.com" /> At the time, the AR-15 was the only rifle that could fulfill a requirement of a "universal" infantry weapon for issue to all services. McNamara ordered its adoption, despite receiving reports of several deficiencies, most notably the lack of a [[Engineering:Chrome plating|chrome-plated]] chamber.<ref name=Sweeney2011>{{cite book|last=Sweeney|first=Patrick|title=Modern Law Enforcement Weapons & Tactics|edition=3rd|url=https://books.google.com/books?id=_4ASmMY9qhoC&pg=PA240|access-date=6 June 2013|date=28 February 2011|publisher=Krause Publications|location=Iola, Wisconsin|isbn=978-1-4402-2684-7|page=240|archive-url=https://web.archive.org/web/20130927004657/http://books.google.com/books?id=_4ASmMY9qhoC&pg=PA240|archive-date=27 September 2013|url-status=live}}</ref><ref name="autogenerated5">{{cite web |url=http://apps.dtic.mil/dtic/tr/fulltext/u2/a953110.pdf|title=Report of the M16 Rifle Review Panel |archive-url=https://web.archive.org/web/20150924123134/http://www.dtic.mil/dtic/tr/fulltext/u2/a953110.pdf |archive-date=24 September 2015 |publisher=Department of the Army |website=Defense Technical Information Center (DTIC) |url-status=live|date=1 June 1968}}</ref>

After modifications (most notably, the charging handle was re-located from under the carrying handle like the AR-10, to the rear of the receiver),<ref name="nodakspud.com" /> the newly redesigned rifle was renamed the ''Rifle, Caliber 5.56&nbsp;mm, M16''.<ref name="autogenerated5" /><ref name="m-14parts.com" /> Inexplicably, the modification to the new M16 did not include a chrome-plated barrel. Meanwhile, the Army relented and recommended the adoption of the M16 for jungle warfare operations. However, the Army insisted on the inclusion of a [[Engineering:Forward assist|forward assist]] to help push the bolt into battery if a cartridge failed to seat into the chamber. The Air Force, Colt, and Eugene Stoner believed that the addition of a forward assist was an unjustified expense. As a result, the design was split into two variants: the Air Force's M16 without the forward assist, and the XM16E1 with the forward assist for the other service branches.

In November 1963, McNamara approved the U.S. Army's order of 85,000 XM16E1s;<ref name="smallarmsreview.com" /><ref>{{harvnb|Rose|2009|pp=380, 392}}</ref> and to appease General LeMay, the Air Force was granted an order for another 19,000 M16s.<ref name="SAOW">{{Cite book|editor=Ezell, Edward Clinton |author1=Smith, Walter H.B.|title=Small Arms of the World|date=May 1990|publisher=Stackpole Books|location=New York|isbn=978-0880296014|pages=46–47|edition=12th}}</ref><ref>{{harvnb|Rose|2009|p=380}}</ref> In March 1964, the M16 rifle went into production and the Army accepted delivery of the first batch of 2,129 rifles later that year, and an additional 57,240 rifles the following year.<ref name="autogenerated5" />

In 1964, the Army was informed that [[Company:DuPont|DuPont]] could not mass-produce the [[Chemistry:Improved Military Rifle#IMR|IMR 4475]] stick powder to the specifications demanded by the M16. Therefore, [[Company:Olin Corporation|Olin Mathieson Company]] provided a high-performance [[Chemistry:Ball propellant|ball propellant]]. While the Olin WC 846 powder achieved the desired {{convert|3300|ft|m|abbr=on}} per second muzzle velocity, it produced much more fouling, which quickly jammed the M16's action (unless the rifle was cleaned well and often).<ref>{{cite news|author=James Fallows|title= M-16: A Bureaucratic Horror Story - Why the rifles jammed|work=The Atlantic|date=June 1981|url=https://www.theatlantic.com/magazine/archive/1981/06/m-16-a-bureaucratic-horror-story/545153|access-date=16 February 2022}}</ref>

[[File:101st Airborne Division - Vietnam 03.jpg|thumb|right|101st Airborne trooper cleans his XM16E1 during the Vietnam War in 1966]]
In March 1965, the Army began to issue the XM16E1 to infantry units. However, the rifle was initially delivered without adequate cleaning kits<ref name="smallarmsreview.com" /> or instructions because advertising from Colt asserted that the M16's materials made the weapon require little maintenance, leading to a misconception that it was capable of self-cleaning.{{Sfn|Rottman|2011|p=20}} Furthermore, cleaning was often conducted with improper equipment, such as [[Chemistry:Insect repellent|insect repellent]], water, and aircraft fuel, which induced further wear on the weapon.{{Sfn|Rottman|2011|p=24}} As a result, reports of stoppages in combat began to surface.<ref name="smallarmsreview.com" /> The most severe problem was known as "failure to extract"—the spent cartridge case remained lodged in the chamber after the rifle was fired.<ref name="smallarmsreview.com" /><ref name=Reliable>{{cite news|author=C.H. Chivers|title=How Reliable is the M16 Rifle?|work={{wipe|The New York Times}}|date=2 November 2009|url=http://atwar.blogs.nytimes.com/2009/11/02/how-reliable-is-the-m-16-rifle/|access-date=12 January 2011|archive-url=https://web.archive.org/web/20110722171947/http://atwar.blogs.nytimes.com/2009/11/02/how-reliable-is-the-m-16-rifle/|archive-date=22 July 2011|url-status=live}}</ref> Documented accounts of dead U.S. troops found next to disassembled rifles eventually led to a Congressional investigation:<ref name="smallarmsreview.com" /><ref name=Time_Under_Fire>{{cite magazine |url=http://www.time.com/time/magazine/article/0,9171,843858,00.html |title=Defense: Under Fire |magazine={{wipe|Time (magazine)}} |issue=9 June 1967 |date=9 June 1967 |access-date=28 September 2009 |archive-url=https://web.archive.org/web/20100501172351/http://www.time.com/time/magazine/article/0,9171,843858,00.html |archive-date=1 May 2010 |url-status=dead}}</ref>

{{Blockquote|We left with 72 men in our platoon and came back with 19, Believe it or not, you know what killed most of us? Our own rifle. Practically every one of our dead was found with his (M16) torn down next to him where he had been trying to fix it.|Marine Corps Rifleman, Vietnam.<ref name=Time_Under_Fire /><ref>{{cite book|url=https://books.google.com/books?id=RyzonQEACAAJ|title=The M16A1 Rifle: Operation and Preventive Maintenance|author1=United States Department of the Army|author2=Robert A. Sadowski|publisher=Skyhorse Publishing|date=2013|access-date=13 July 2014|isbn=978-1-61608-864-4|archive-url=https://web.archive.org/web/20190326191809/https://books.google.com/books/about/The_M16A1_Rifle.html%3Fid%3DRyzonQEACAAJ|archive-date=26 March 2019|url-status=live}}</ref>}}

In February 1967, the improved XM16E1 was standardized as the M16A1.<ref name=SAOW /> The new rifle had a chrome-plated chamber and bore to eliminate corrosion and stuck cartridges, and other minor modifications.<ref name="smallarmsreview.com" /> New cleaning kits, powder solvents, and lubricants were also issued. Intensive training programs in weapons cleaning were instituted including a comic book-style operations manual.{{Sfn|Rottman|2011|p=79}}<ref>{{Cite book|url=https://archive.org/stream/DaPam750-30/M16a1-ComicBook-MaintenanceManual_djvu.txt |title=Full text of "DA Pam 750-30"|date=28 June 1968|access-date=13 July 2014}}</ref> As a result, reliability problems were largely resolved and the M16A1 rifle achieved widespread acceptance by U.S. troops in Vietnam.<ref name="smallarmsreview.com" /><ref name="a953117">{{citation|url=http://apps.dtic.mil/dtic/tr/fulltext/u2/a953117.pdf|title=Report of the M16 Review Panel|date=1 June 1968|series=M16 Surveys in the Republic of Vietnam|website=Department of the Army|publisher=Office of the Deputy Chief of Staff for Research, Development, Acquisition|location=Washington DC|access-date=3 June 2019|archive-url=https://web.archive.org/web/20160304023922/http://www.dtic.mil/dtic/tr/fulltext/u2/a953117.pdf|archive-date=4 March 2016|url-status=live}}</ref>

In 1969, the M16A1 officially replaced the M14 rifle to become the U.S. military's standard [[Engineering:Service rifle|service rifle]].<ref name="SAOW2" /><ref name="Urdang, p. 801" /> In 1970, the new WC 844 powder was introduced to reduce fouling.<ref name=dew>{{cite web|url=http://www.thegunzone.com/556prop.html|title=The Great Propellant Controversy|last1=Watters|first1=Daniel E.|work=The Gun Zone|access-date=29 June 2013|archive-url=https://web.archive.org/web/20130722235300/http://www.thegunzone.com/556prop.html|archive-date=22 July 2013|url-status=dead}}</ref>

Colt, H&R, and GM Hydramatic Division manufactured M16A1 rifles during the Vietnam War.{{citation needed|date=December 2022}} M16s were produced by Colt until the late 1980s when FN Herstal (FN USA) began to manufacture them.<ref>{{cite news|url=https://www.nytimes.com/1988/10/03/nyregion/army-drops-colt-as-m16-rifle-maker.html?mtrref=www.google.com&gwh=F9079A7EB4217F8F19E06C9FDBD1F9BB&gwt=pay|archive-url=https://web.archive.org/web/20190425222441/https://www.nytimes.com/1988/10/03/nyregion/army-drops-colt-as-m16-rifle-maker.html?mtrref=www.google.com&gwh=F9079A7EB4217F8F19E06C9FDBD1F9BB&gwt=pay|url-status=dead|archive-date=25 April 2019|title=Army Drops Colt as M16 Rifle Maker|work=The New York Times|date=3 October 1988}}</ref>

==Reliability==
[[File:DIRECTM16.gif|thumb|The M16 gas redirect system, incorrectly labeled as direct impingement. The gif does not show the operating mechanism of the rifle, only the gas redirect system.]]
During the early part of its service, the M16 had a reputation for poor reliability and a malfunction rate of two per 1000 rounds fired.<ref name="Hearings 1969">Hearings, Reports and Prints of the House Committee on Armed Services, Issue 14, Part 1. United States. Congress. House. Committee on Armed Services. U.S. Government Printing Office. 1969. p. 2326.</ref> The M16's action works by passing high-pressure propellant gasses, tapped from the barrel, down a tube and into the carrier group within the upper receiver. The gas goes from the gas tube, through the bolt carrier key, and into the inside of the carrier where it expands in a donut-shaped gas-piston cylinder. Because the bolt is prevented from moving forward by the barrel, the carrier is driven to the rear by the expanding gases and thus converts the energy of the gas to the movement of the rifle's parts. The back part of the bolt forms a piston head and the cavity in the bolt carrier is the piston sleeve. While the M16 is commonly said to use a [[Engineering:Direct impingement|direct impingement]] system, this is wrong, and it is instead correct to say it uses an ''internal piston'' system.<ref name="armalite1">{{cite web |url=http://www.armalite.com/images/Tech%20Notes%5CTech%20Note%2054,%20Gas%20vs%20Op%20Rod%20Drive,%20020815.pdf |title=ARMALITE TECHNICAL NOTE 54: DIRECT IMPINGEMENT VERSUS PISTON DRIVE |archive-url=https://wayback.archive-it.org/all/20120905024032/http://www.armalite.com/images/Tech%20Notes%5CTech%20Note%2054,%20Gas%20vs%20Op%20Rod%20Drive,%20020815.pdf |archive-date=5 September 2012|website=Armalite|date=3 July 2010}}</ref>

This design is much lighter and more compact than a gas-piston design. However, this design requires that combustion byproducts from the discharged cartridge be blown into the receiver as well. This accumulating carbon and vaporized metal build-up within the receiver and bolt carrier negatively affects reliability and necessitates more intensive maintenance on the part of the individual soldier. The channeling of gasses into the bolt carrier during operation increases the amount of heat that is deposited in the receiver while firing the M16 and causes the essential lubricant to be "burned off". This requires frequent and generous applications of appropriate lubricant.<ref name="ReferenceA" /> Lack of proper lubrication is the most common source of weapon stoppages or jams<!--in general, or in M16's?-->.<ref name="ReferenceA" />

The original M16 fared poorly in the jungles of Vietnam and was infamous for reliability problems in harsh environments. Max Hastings was very critical of the M16's general field issue in Vietnam just as grievous design flaws were becoming apparent. He further states that the Shooting Times experienced repeated malfunctions with a test M16 and assumed these would be corrected before military use, but they were not. Many Marines and soldiers were so angry with the reliability problems they began writing home and on 26 March 1967, the Washington Daily News broke the story.<ref>{{cite book |last1=Hastings |first1=Max |title=Vietnam, an epic tragedy 1945 - 1975 |date=2018 |publisher=Collins |isbn=978-0-00-813298-9 |pages=350 to 354}}</ref> Eventually, the M16 became the target of a Congressional investigation.<ref>{{cite book|last=Kahaner|first=Larry |title=AK-47: The Weapon that Changed the Face of War|year=2007|publisher=Wiley|isbn=978-0-470-16880-6|page=236|quote=This was dubbed the Ichord hearings after Missouri representative Richard Ichord, who championed Congress's inquiry into failures of the M-16 during the Vietnam War.}}</ref>

The investigation found that:<ref name="autogenerated5" />
* The M16 was issued to troops without cleaning kits or instructions on how to clean the rifle.
* The M16 and 5.56×45&nbsp;mm cartridge was tested and approved with the use of a DuPont IMR8208M [[Chemistry:Improved Military Rifle|extruded powder]], which was switched to Olin Mathieson WC846 ball powder which produced much more fouling, which quickly jammed the action of the M16 (unless the gun was cleaned well and often).
* The M16 lacked a [[Engineering:Forward assist|forward assist]] (rendering the rifle inoperable when it failed to go fully forward).
* The M16 lacked a chrome-plated chamber, which allowed corrosion problems and contributed to case extraction failures (which was considered the most severe problem and required extreme measures to clear, such as inserting the cleaning rod down the barrel and knocking the spent cartridge out).

[[File:Front cover - the M16A1 Rifle - Operation and Preventive Maintenance (art by Will Eisner).jpg|thumb|right|Front cover – ''The M16A1 Rifle – Operation and Preventive Maintenance'' by Will Eisner, issued to American soldiers in the Vietnam War.]]
When these issues were addressed and corrected by the M16A1, the reliability problems decreased greatly.<ref name="SAOW" /> According to a 1968 Department of Army report, the M16A1 rifle achieved widespread acceptance by U.S. troops in Vietnam.<ref name="a953117" /> "Most men armed with the M16 in Vietnam rated this rifle's performance high, however, many men entertained some misgivings about the M16's reliability. When asked what weapon they preferred to carry in combat, 85 percent indicated that they wanted either the M16 or its [smaller] carbine-length version, the XM177E2." Also, "the M14 was preferred by 15 percent, while less than one percent wished to carry either the [[Engineering:Stoner 63|Stoner rifle]], the AK-47, the [M1] carbine or a pistol."<ref name="a953117" /> In March 1970, the "President's Blue Ribbon Defense Panel" concluded that the issuance of the M16 saved the lives of 20,000 U.S. servicemen during the Vietnam War, who would have otherwise died had the M14 remained in service.<ref name="pogoarchives.org">{{cite web |author1=Hallock, Colonel Richard R. (retired) US Army |url=http://pogoarchives.org/labyrinth/09/02.pdf |title=M16 Case Study |archive-url=https://web.archive.org/web/20150906090843/http://pogoarchives.org/labyrinth/09/02.pdf |archive-date=6 September 2015 |date=16 March 1970|website=Pogo Archives.org}}</ref> However, the M16 rifle's reputation has suffered as of 2011.{{why|date=August 2023|reason=What happened in 2011?}}<ref name="SAOW" />{{Sfn|Rottman|2011|p=30}}

Another underlying cause of the M16's jamming problem was identified by ordnance staff that discovered that Stoner and ammunition manufacturers had initially tested the AR-15 using DuPont IMR8208M extruded (stick) powder. Later ammunition manufacturers adopted the more readily available Olin Mathieson WC846 ball powder. The ball powder produced a longer peak chamber pressure with undesired timing effects. Upon firing, the cartridge case expands and seals the chamber ([[Engineering:Obturation|obturation]]). When the peak pressure starts to drop the cartridge case contracts and then can be extracted. With ball powder, the cartridge case was not contracted enough during extraction due to the longer peak pressure period. The ejector would then fail to extract the cartridge case, tearing through the case rim, and leaving an obturated case behind.<ref>{{Cite web|title=History of the .223 Remington Cartridge|url=https://fenixammo.com/pages/history-of-the-223-remington-cartridge|access-date=25 April 2021|website=Fenix Ammunition|language=en}}</ref>

After the introduction of the M4 carbine, it was found that the shorter barrel length of 14.5&nbsp;inches also harms the reliability, as the gas port is located closer to the chamber than the gas port of the standard length M16 rifle: 7.5&nbsp;inches instead of 13&nbsp;inches.<ref name="armalite.com">{{cite web |url= http://www.armalite.com/images/Tech%20Notes%5CTech%20Note%2048,%20Barrel%20Design,%20Heat,%20and%20Reliability,%20030824%E2%80%A6.pdf |title=Technical note 48: the effects of barrel design and heat on reliability|archive-url=https://web.archive.org/web/20111111015504/http://www.armalite.com/images/Tech%20Notes/Tech%20Note%2048%2C%20Barrel%20Design%2C%20Heat%2C%20and%20Reliability%2C%20030824%E2%80%A6.pdf |archive-date=11 November 2011 |website=Armalite |date=24 August 2003 |url-status=dead}}</ref> This affects the M4's timing and increases the amount of stress and heat on the critical components, thereby reducing reliability.<ref name="armalite.com" /> In a 2002 assessment, the USMC found that the M4 malfunctioned three times more often than the M16A4 (the M4 failed 186 times for 69,000 rounds fired, while the M16A4 failed 61 times).<ref name="defenseindustrydaily.com">{{cite web |url=http://www.defenseindustrydaily.com/the-usas-m4-carbine-controversy-03289/ |title=The USA's M4 Carbine Controversy|archive-url=https://web.archive.org/web/20070713081000/http://www.defenseindustrydaily.com/the-usas-m4-carbine-controversy-03289/ |archive-date=13 July 2007 |website=Defense Industry Daily|date=21 November 2011|access-date=24 December 2011|url-status=live}}</ref> Thereafter, the Army and Colt worked to make modifications to the M4s and M16A4s to address the problems found.<ref name="defenseindustrydaily.com" /> In tests conducted in 2005 and 2006 the Army found that on average, the new M4s and M16s fired approximately 5,000 rounds between stoppages.<ref name="defenseindustrydaily.com" /><ref>{{cite web |url=https://apps.dtic.mil/sti/pdfs/ADA429392.pdf|title=A COMPARATIVE ANALYSIS OF CURRENT AND PLANNED SMALL ARMS WEAPON SYSTEMS|author1= Jenkins, Shawn T., Major, United States Army |author2= Lowrey, Douglas S., Major, United States Army |publisher=Submitted in partial fulfillment of the requirements for the degree of MASTER OF BUSINESS ADMINISTRATION |website=NAVAL POSTGRADUATE SCHOOL|date=December 2004 |archive-url=https://web.archive.org/web/20130722234329/http://www.dtic.mil/cgi-bin/GetTRDoc?AD=ADA429392 |archive-date=22 July 2013 |access-date=20 November 2015|url-status=live}}</ref>

In December 2006, the Center for Naval Analyses (CNA) released a report on U.S. small arms in combat. The CNA conducted surveys on 2,608 troops returning from combat in Iraq and Afghanistan over the past 12 months. Only troops who had fired their weapons at enemy targets were allowed to participate. 1,188 troops were armed with M16A2 or A4 rifles, making up 46 percent of the survey. 75 percent of M16 users (891 troops) reported they were satisfied with the weapon. 60 percent (713 troops) were satisfied with handling qualities such as handguards, size, and weight. Of the 40 percent dissatisfied, most were with its size. Only 19 percent of M16 users (226 troops) reported a stoppage, while 80 percent of those that experienced a stoppage said it had little impact on their ability to clear the stoppage and re-engage their target. Half of the M16 users experienced failures in their magazines to feed. 83 percent (986 troops) did not need their rifles repaired while in the theater. 71 percent (843 troops) were confident in the M16's reliability, defined as a level of soldier confidence their weapon will fire without malfunction, and 72 percent (855 troops) were confident in its durability, defined as a level of soldier confidence their weapon will not break or need repair. Both factors were attributed to high levels of soldiers performing their maintenance. 60 percent of M16 users offered recommendations for improvements. Requests included greater bullet lethality, newly-built instead of rebuilt rifles, better quality magazines, decreased weight, and a collapsible stock. Some users recommended shorter and lighter weapons such as the [[Engineering:M4 carbine|M4 carbine]].<ref>{{cite journal |url=http://images.military.com/pix/defensetech/cna_m4_study_d0015259_a2.pdf |first=Sara M. |last=Russell |title=Soldier Perspectives on Small Arms in Combat |publisher=CNA Corporation |date=December 2006 |access-date=13 July 2014 |url-status=dead |archive-url=https://web.archive.org/web/20150831150054/http://images.military.com/pix/defensetech/cna_m4_study_d0015259_a2.pdf |archive-date=31 August 2015}}</ref> Some issues have been addressed with the issuing of the [[Engineering:STANAG magazine#Issues and improvements|Improved STANAG magazine]] in March 2009,<ref>{{cite web |url=http://www.thefirearmblog.com/blog/2009/06/13/brownells-shipping-m16-magazines-with-anti-tilt-follower-to-military/ |title=Brownells shipping M16 magazines with anti-tilt follower to military|archive-url=https://web.archive.org/web/20130921053406/http://www.thefirearmblog.com/blog/2009/06/13/brownells-shipping-m16-magazines-with-anti-tilt-follower-to-military/ |archive-date=21 September 2013 |website=The Firearm Blog|date=13 June 2009}}</ref><ref>{{cite web |url=http://www.thefirearmblog.com/blog/2009/12/16/new-us-army-m16-tan-magazine/ |title=New US Army M16 "Tan" Magazine|archive-url=https://web.archive.org/web/20130921053924/http://www.thefirearmblog.com/blog/2009/12/16/new-us-army-m16-tan-magazine/ |archive-date=21 September 2013 |website=The Firearm Blog|date=16 December 2009}}</ref> and the [[Engineering:5.56×45mm NATO#M855A1|M855A1 Enhanced Performance Round]] in June 2010.<ref name="EPR">{{cite web |url=http://www.pica.army.mil/PicatinnyPublic/highlights/archive/2010/06-24-10.asp |title=Army begins shipping improved 5.56mm cartridge|archive-url=https://web.archive.org/web/20130601185932/http://www.pica.army.mil/PicatinnyPublic/highlights/archive/2010/06-24-10.asp |archive-date=1 June 2013|website=Picatinny Arsenal |date=24 June 2010}}</ref>

In early 2010, two journalists from ''{{wipe|The New York Times}}'' spent three months with soldiers and Marines in Afghanistan. While there, they questioned around 100 infantry troops about the reliability of their M16 rifles, as well as the M4 carbine. The troops did not report reliability problems with their rifles. While only 100 troops were asked, they engaged in daily fighting in Marja, including at least a dozen intense engagements in Helmand Province, where the ground is covered in fine powdered sand (called "moon dust" by troops) that can stick to firearms.<ref name="atwar.blogs.nytimes.com">{{cite news |url=http://atwar.blogs.nytimes.com/2010/07/07/examining-the-complaints-about-american-rifle-reliability/?_r=0 |title=Examining the Complaints About American Rifle Reliability|archive-url=https://web.archive.org/web/20130922150652/http://atwar.blogs.nytimes.com/2010/07/07/examining-the-complaints-about-american-rifle-reliability/?_r=0 |archive-date=22 September 2013 |work=The New York Times|date=7 July 2010}}</ref> Weapons were often dusty, wet, and covered in mud. Intense firefights lasted hours with several magazines being expended. Only one soldier reported a jam when his M16 was covered in mud after climbing out of a canal. The weapon was cleared and resumed firing with the next chambered round. Furthermore, the Marine Chief Warrant Officer responsible for weapons training and performance of the Third Battalion, Sixth Marines, reported that "We've had nil in the way of problems; we've had no issues", with his battalion's 350 M16s and 700 M4s.<ref name="atwar.blogs.nytimes.com" />

==Design==
[[File:Rifle 5.56mm, XM16E1, Operation and Cycle of Functioning TF9-3663.webm|thumb|Video...Rifle 5.56mm, XM16E1. Operation and Cycle of Functioning.]]
[[File:M16 rifle Firing FM 23-9 Fig 2-7.png|thumb|M16 internal piston action system]]

The M16 is a lightweight, 5.56&nbsp;mm, air-cooled, [[Engineering:Gas-operated reloading|gas-operated]], [[Engineering:Magazine (firearms)|magazine]]-fed [[Engineering:Assault rifle|assault rifle]], with a [[Engineering:Rotating bolt|rotating bolt]]. The M16's receivers are made of [[Chemistry:7075 aluminium alloy|7075 aluminum alloy]], its barrel, bolt, and bolt carrier of steel, and its handguards, pistol grip, and buttstock of plastics.

The M16 internal piston action was derived from the original ArmaLite AR-10 and ArmaLite AR-15 actions. This internal piston action system designed by Eugene Stoner is commonly called a direct impingement system, but it does not use a conventional direct impingement system. In {{US Patent|2951424}}, the designer states: ″This invention is a true expanding gas system instead of the conventional impinging gas system.″<ref>{{cite web |url=http://www.google.com/patents?id=ETJjAAAAEBAJ&printsec=abstract&zoom=4#v=onepage&q&f=false |title=Patent US2951424 - GAS OPERATED BOLT AND CARRIER SYSTEM |access-date=11 April 2013 }}{{Dead link|date=February 2022 |bot=InternetArchiveBot |fix-attempted=yes }}</ref>
The gas system, bolt carrier, and bolt-locking design is ammunition specific, since it does not have an adjustable gas port or valve to adjust the weapon to various propellant and projectile or barrel length specific pressure behavior.

The M16A1 was especially lightweight at {{convert|7.9|lb|kg}} with a loaded 30-round magazine.<ref name="flii.by">[https://web.archive.org/web/20210225034309/http://flii.by/file/34705/jruxixos92.html Operator's Manual M16A1 Rifle] . flii.by</ref> This was significantly less than the M14 that it replaced at {{convert|10.7|lb|kg}} with a loaded 20-round magazine.<ref>{{Cite web|url=http://www.m14.ca/FM/FM23_8A.pdf|archive-url=https://web.archive.org/web/20150418000847/http://www.m14.ca/FM/FM23_8A.pdf|url-status=dead|title=Field Manual No. 23-8, U.S. RIFLE 7.62MM, Ml4 AND M14E2, HEADQUARTERS, DEPARTMENT OF THE ARMY, Washington, D.C., 7 May 1966|archive-date=18 April 2015}}</ref> It is also lighter when compared to the [[Engineering:AKM|AKM]]'s {{convert|8.3|lb|kg}} with a loaded 30-round magazine.<ref name="scribd2">{{cite web |url=https://www.scribd.com/doc/38483061/Ak-47-Technical-Description-Manual |title=Ak 47 Technical Description – Manual |publisher=Scribd.com |date=30 September 2010 |access-date=23 August 2012 |archive-url=https://web.archive.org/web/20120328103151/http://www.scribd.com/doc/38483061/Ak-47-Technical-Description-Manual |archive-date=28 March 2012 |url-status=live}}</ref>

The M16A2 weighs {{convert|8.8|lb|kg|1|abbr=on}} loaded with a 30-round magazine, because of the adoption of a thicker barrel profile. The thicker barrel is more resistant to damage when handled roughly and is also slower to overheat during sustained fire. Unlike a traditional "bull" barrel that is thick its entire length, the M16A2's barrel is only thick forward of the handguards. The barrel profile under the handguards remained the same as the M16A1 for compatibility with the [[Engineering:M203 grenade launcher|M203 grenade launcher]].

===Barrel===
Early model M16 barrels had a [[Engineering:Rifling|rifling]] twist of four grooves, right-hand [[Twist rate|twist]], one turn in 14&nbsp;inches (1:355.6&nbsp;mm or 64 calibers) bore—as it was the same rifling as used by the .222 Remington sporting cartridge. After finding out that under unfavorable conditions, military bullets could yaw in flight at long ranges, the rifling was soon altered. Later M16 models and the M16A1 had an improved rifling with six grooves, right-hand twist, one turn in 12&nbsp;inches (1:304.8&nbsp;mm or 54.8 calibers) for increased accuracy and was optimized to adequately stabilize the M193 ball and M196 tracer bullets. M16A2 and current models are optimized for firing the heavier NATO SS109 ball and long L110 tracer bullets and have six grooves, right-hand twist, one turn in 7 in (1:177.8&nbsp;mm or 32 calibers).<ref>{{cite web |last=Simpson |first=Layne |url=http://www.shootingtimes.com/2011/01/04/ammunition_st223_120606/ |title=Handloading The .223 Remington for the AR-15 |publisher=Shootingtimes.com |date=4 January 2011 |access-date=13 July 2014 |archive-url=https://web.archive.org/web/20131203004627/http://www.shootingtimes.com/2011/01/04/ammunition_st223_120606/ |archive-date=3 December 2013 |url-status=live}}</ref><ref name="auto3">{{Cite book|url=https://archive.org/stream/ArmyTechnicalManualforM16Rifle-Tm9-1005-249-23p/Manual-Tm9-1005-249-23p#page/n9/mode/2up |title=Army Technical Manual (for M16 rifle) – TM 9-1005-249-23P |publisher=United States Army |via=Archive.org |access-date=13 July 2014}}</ref><ref name="Colt_Weapon_Systems"/><ref>Military Small Arms of the 20th Century, 7th Edition, 2000 by Ian V. Hogg & John S. Weeks. P 292</ref><ref name="auto">{{cite web |last= |first= |url=https://www.inetres.com/gp/military/infantry/rifle/556mm_ammo.html |title=5.56mm (5.56 x 45 mm) Ammunition |publisher=netres.comm |date=3 May 2001 |access-date=18 February 2022 }}</ref>

M193 ball and M196 tracer bullets may be fired in a rifle with a one turn in 7 in (1:177.8&nbsp;mm or 32 calibers) twist barrel.  NATO SS109 ball and L110 tracer bullets should only be used in emergency situations at ranges under {{convert|90|m|yd|0|abbr=on}} with a one turn in 12&nbsp;inches (1:304.8&nbsp;mm or 54.8 calibers) twist, as this twist is insufficient to stabilize these projectiles.<ref name="auto"/>
Weapons designed to adequately stabilize both the M193 or SS109 projectiles (like civilian market clones) usually have a six-groove, right-hand twist, one turn in 9&nbsp;inches (1:228.6&nbsp;mm or 41.1 calibers) or one turn in 8&nbsp;inches (1:203.2&nbsp;mm or 36.5 calibers) bore, although other and 1:7&nbsp;inches twist rates are available as well.

===Recoil===
{{blockquote|The (M16's) Stoner system provides a very symmetric design that allows straight-line movement of the operating components. This allows recoil forces to drive straight to the rear. Instead of connecting or other mechanical parts driving the system, high-pressure gas performs this function, reducing the weight of moving parts and the rifle as a whole.<ref name="armalite1" />}}
The M16 uses a "straight-line" recoil design, where the recoil spring is located in the stock directly behind the action,<ref name="SAOW2" /> and serves the dual function of operating spring and recoil buffer.<ref name="SAOW2" /> The stock being in line with the bore also reduces muzzle rise, especially during automatic fire. Because recoil does not significantly shift the point of aim, faster follow-up shots are possible and user fatigue is reduced. In addition, current model M16 flash-suppressors also act as compensators to reduce recoil further.<ref name="quarterbore.com">{{cite web|date=5 June 2003|orig-year=August 1986|title=Operator's Manual w/ Components List|url=http://quarterbore.com/library/pdf_files/tm43-0001-27.pdf|url-status=dead|archive-url=https://web.archive.org/web/20030605100247/http://quarterbore.com/library/pdf_files/tm43-0001-27.pdf|archive-date=5 June 2003|series=Rifle, 5.56-MM, M16A2 W/E (1005-01-128-9936)|publisher=United States Department of the Army}}</ref>

{| class="wikitable" style="margin: 1em auto; text-align:center; width:350px;"
|-
! colspan=2 |Free recoil<ref name="kwk.us">{{cite web|url=http://kwk.us/recoil.html|title=Recoil Calculator|website=kwk.us|access-date=3 June 2019|archive-url=https://web.archive.org/web/20181017223016/http://kwk.us/recoil.html|archive-date=17 October 2018|url-status=live}}</ref>
|-
!
! M16
|-
|'''Momentum'''
| style=|40.4&nbsp;lb-ft/s
|-
|'''Velocity'''
| style=|{{convert|5.1|ft/s|m/s|abbr=on}}
|-
|'''Energy'''
| style=|{{convert|3.2|ftlb|J|abbr=on|adj=off}}
|}
Notes: Free recoil is calculated by using the rifle weight, bullet weight, muzzle velocity, and charge weight.<ref name="kwk.us" /> It is that which would be measured if the rifle were fired suspended from strings, free to recoil.<ref name="kwk.us" /> A rifle's perceived recoil is also dependent on many other factors which are not readily quantified.<ref name="kwk.us" />

===Sights===
[[File:M16 rifle correct sight picture fig 4-18.png|thumb|M16 sight picture when using the {{convert|0.070|in|mm|2|abbr=on}} rear aperture]]
[[File:M16A2 rear sight in front side P1010034.JPG|thumb|M16A2 with unmarked aperture rear sight for normal firing situations raised. The larger aperture, marked '0-2', is flipped down.]]
[[File:M16 upper right.jpg|thumb|Fully adjustable rear sight, brass deflector and forward assist of the M16A2]]

The M16's most distinctive ergonomic feature is the carrying handle and rear sight assembly on top of the receiver. This is a by-product of the original AR-10 design, where the carrying handle contained a rear sight that could be set for specific range settings and also served to protect the charging handle.<ref name=SAOW2>{{Cite book |editor=Ezell, Edward Clinton |author1=Smith, Walter H.B.|title= Small Arms of the World |date=May 1990|publisher=Stackpole Books |location=New York |isbn=978-0880296014 |pages=746–762|edition=12th}}</ref>
The M16 carry handle also provided mounting groove interfaces and a hole at the bottom of the handle groove for mounting a Colt 3×20 [[Engineering:Telescopic sight|telescopic sight]] featuring a [[Engineering:Telescopic sight#Bullet drop compensation|Bullet Drop Compensation]] elevation adjustment knob for ranges from {{convert|100|to|500|yd|m|0|abbr=on}}. This concurs with the pre-M16A2 maximum effective range of {{convert|460|m|yd|0|abbr=on}}.<ref name="auto3"/> The Colt 3×20 telescopic sight was factory adjusted to be parallax-free at {{convert|200|yd|m|0|abbr=on}}.<ref>{{cite web| url = http://pullig.dyndns.org/retroblackrifle/ModGde/Aces/LateColt3x.html| title = Early Colt 3× scope| access-date = 28 March 2021| archive-date = 23 September 2021| archive-url = https://web.archive.org/web/20210923034635/http://pullig.dyndns.org/retroblackrifle/ModGde/Aces/LateColt3x.html| url-status = dead}}</ref><ref>{{cite web| url = http://pullig.dyndns.org/retroblackrifle/ModGde/Aces/LateColt3x.html| title = Late Colt 3× scope| access-date = 28 March 2021| archive-date = 23 September 2021| archive-url = https://web.archive.org/web/20210923034635/http://pullig.dyndns.org/retroblackrifle/ModGde/Aces/LateColt3x.html| url-status = dead}}</ref> In Delft, the Netherlands Artillerie-Inrichtingen produced a roughly similar 3×25 telescopic sight for the carrying handle mounting interfaces.<ref>{{cite web| url = http://pullig.dyndns.org/retroblackrifle/ModGde/Aces/Delft.html| title = Delft 325 scope| access-date = 29 March 2021| archive-date = 23 September 2021| archive-url = https://web.archive.org/web/20210923021215/http://pullig.dyndns.org/retroblackrifle/ModGde/Aces/Delft.html| url-status = dead}}</ref>
	
The M16 elevated iron sight line has a {{convert|19.75|in|mm|0|abbr=on}} sight radius.<ref name="Colt_Weapon_Systems"/> As the M16 series rear sight, front sight and sighting in targets designs were modified over time and non-iron sight (optical) aiming devices and new service ammunition were introduced zeroing procedures changed.<ref name="auto1">{{cite web |url=https://armarksman.files.wordpress.com/2018/02/3-zero-new-process.pdf |website=ArmyReserveMarksman.info |title=New Zeroing Procedures |access-date=8 February 2022}}</ref>

The standard pre-M16A2 "Daylight Sight System" uses an [[Engineering:ArmaLite AR-15#Design details|AR-15-style]] L-type flip, two [[Engineering:Iron sights#Aperture sights|aperture rear sight]] featuring two combat settings: short-range {{convert|0|to|300|m|yd|0|abbr=on}} and long-range {{convert|300|to|400|m|yd|0|abbr=on}}, marked 'L'.<ref>{{cite web |url=https://archive.org/details/OperatorsManualForM16M16a1/page/n45/mode/2up?view=theater |website=Operator's Manual For M16, M16A1 |title=Initial Adjustments - Standard Daylight Sight System |format=Section II |pages=2–16|access-date=27 September 2011}}</ref>
The pre-M16A2 "Daylight Sight System" short-range and long-range zeros are {{convert|250|and|375|m|yd|0|abbr=on}} with M193 ammunition.<ref>{{cite web |url=https://archive.org/details/OperatorsManualForM16M16a1/page/n49/mode/2up?view=theater |website=Operator's Manual For M16, M16A1 |title=Initial Adjustments - Standard Daylight Sight System |format=Section II |pages=2–19|access-date=27 September 2011}}</ref> The rear sight features a windage drum that can be adjusted during zeroing with about 1 MOA increments. The front sight is a tapered round post of approximately {{convert|0.0625|in|mm|2|abbr=on}} diameter adjustable during zeroing in about 1 [[Minute and second of arc#Firearms|MOA]] increments. A cartridge or tool is required to (re)zero the sight line.<ref>{{cite web |url= https://www.bevfitchett.us/army-m16-marksmanship/mal-standard-sights-and-zeroing.html| title = M16Al Standard Sights And Zeroing| date = 26 April 2022}}</ref><ref name="auto1"/><ref name="auto2">{{cite web |url=https://archive.org/details/OperatorsManualForM16M16a1/page/n49/mode/2up?view=theater |website=Operator's Manual For M16, M16A1|title= 2-20 Initial Adjustments - Sight Adjustment (Low Light Level and Standard Daylight Systems |format=Section II |pages=2–20|access-date=8 October 2011}}</ref>

An alternative pre-M16A2 "Low Light Level Sight System", includes a front sight post with a weak light source provided by [[Earth:Tritium radioluminescence|tritium radioluminescence]] in an embedded small glass vial and a two aperture rear sight consisting of a {{convert|2|mm|in|3|abbr=on}} diameter aperture marked 'L' intended for normal use out to {{convert|460|m|yd|0|abbr=on}} and a {{convert|7|mm|in|3|abbr=on}} diameter large aperture for night firing.<ref>{{cite web |url=https://archive.org/stream/OperatorsManualForM16M16a1#page/n47/mode/2up |website=Operator's Manual For M16, M16A1|title= 2-17 Initial Adjustments - Low Light Level Sight System |format=Section II |pages=2–17|access-date=8 October 2011}}</ref> Regulation stipulates the radioluminescent front sight post must be replaced if more than 144 months (12 years) elapsed after manufacture.<ref>{{Cite book|url=https://archive.org/details/ArmyTechnicalManualforM16Rifle-Tm9-1005-249-23p/page/n145/mode/2up?view=theater |title=Army Technical Manual (for M16 rifle) – TM 9-1005-249-23P |publisher=United States Army |via=Archive.org |access-date=13 July 2014}}</ref> The "Low Light Level Sight System" elevation and windage adjustment increments are somewhat coarser compared to the "Daylight Sight System".<ref name="auto2"/>

With the advent of the M16A2, a less simple fully adjustable rear sight was added, allowing the rear sight to be dialed in with an elevation wheel for specific range settings between {{convert|300|and|800|m|yd|0|abbr=on}} in 100 m increments and to allow windage adjustments with a windage knob without the need of a cartridge or tool. The unmarked approximately {{convert|0.070|in|mm|2|abbr=on}} diameter aperture rear sight is for normal firing situations, zeroing and with the elevation knob for target distances up to 800 meters. The downsides of relatively small rear sight apertures are less light transmission through the aperture and a reduced field of view. A new larger approximately {{convert|0.2|in|mm|2|abbr=on}} diameter aperture, marked '0-2' and featuring a windage setting index mark, offers a larger field of view during battle conditions and is used as a ghost ring for quick target engagement and during limited visibility. When flipped down, the engraved windage mark on top of the '0-2' aperture ring shows the dialed in windage setting on a windage scale at the rear of the rear sight assembly. When the normal use rear aperture sight is zeroed at 300 m with SS109/M855 ammunition, first used in the M16A2, the '0-2' rear sight will be zeroed for 200 m. The front sight post was widened to approximately {{convert|0.075|in|mm|2|abbr=on}} diameter and became square and became adjustable during zeroing in about 1.2 MOA increments.<ref>{{cite web|url=https://www.ar15.com/content/webPDF/TM9-1005-319-10.pdf |title=TM 9-1005-319-10 (2010) - Operator's Manual for Rifle, 5.56 MM, M16A2/M16A3/M4 (Battlesight Zero pages 48-55)|access-date=3 June 2014}}</ref><ref name="Venola, Richard 2005">{{cite magazine |author1=Venola, Richard |date=2005|title=What a Long Strange Trip It's Been |magazine=Book of the AR-15 |volume=1 |edition=2nd |pages=6–18}}</ref><ref>{{cite web|url=https://thenewrifleman.com/the-ultimate-guide-to-the-ar15-iron-sights/|title=The Ultimate Guide to the AR15 Iron Sights Ver 1.1|date=16 May 2016 |access-date=4 February 2022}}</ref>

The M16A4 omitted the carrying handle and rear sight assembly on top of the receiver. Instead, it features a MIL-STD-1913 [[Engineering:Picatinny rail|Picatinny rail]]ed flat-top upper receiver for mounting various optical sighting devices or a new detachable carrying handle and M16A2-style rear sight assembly.
The current U.S. Army and Air Force issue M4(A1) Carbine comes with the M68 Close Combat Optic and Back-up Iron Sight.<ref>{{cite web |url=http://www.armedforces-int.com/article/m68-close-combat-optic.html |title=Company's Successful M68 Close Combat Optic Standard Issue Equipment For US Forces Since 1997 |author1=Henderson, Ronald |archive-url=https://web.archive.org/web/20111209112859/http://armedforces-int.com/article/m68-close-combat-optic.html |archive-date=9 December 2011|website=Armed Forces International |access-date=9 February 2012|url-status=dead}}</ref><ref>{{cite journal |url=http://www.saffm.hq.af.mil/shared/media/document/AFD-070221-136.pdf |title=Fiscal Year (FY) 2005 BUdget Estimates: Procurement of Ammunition |publisher={{wipe|United States Department of the Air Force}} |date=February 2004 |access-date=13 July 2014 |url-status=dead |archive-url=https://web.archive.org/web/20130922090233/http://www.saffm.hq.af.mil/shared/media/document/AFD-070221-136.pdf |archive-date=22 September 2013}}</ref> The U.S. Marine Corps uses the 4×32 [[Engineering:Advanced Combat Optical Gunsight|ACOG]] Rifle Combat Optic<ref>{{cite web |url=http://www.trijicon.com/na_en/company/history.php |title=History – Trijicon, Inc|archive-url=https://web.archive.org/web/20120630182033/http://www.trijicon.com/na_en/company/history.php |archive-date=30 June 2012 |website=Trijicon.com|access-date=9 February 2012|url-status=live}}</ref><ref>{{cite web |url=http://www.defenseindustrydaily.com/marines-pleased-so-usmc-orders-660m-more-acog-rifle-scopes-01021/ |title=Marines Pleased, So USMC Orders $660M More ACOG Rifle Scopes|archive-url=https://web.archive.org/web/20121122062124/http://www.defenseindustrydaily.com/marines-pleased-so-usmc-orders-660m-more-acog-rifle-scopes-01021/ |archive-date=22 November 2012 |website=Defense Industry Daily |date=15 August 2005|access-date=9 February 2012|url-status=live}}</ref> and the U.S. Navy uses the [[Company:EOTech|EOTech]] [[Physics:Holographic weapon sight|Holographic Weapon Sight]].<ref>{{cite web |url=http://www.tactical-life.com/online/special-weapons/colts-m4a1-556mm-carbine/ |title=Colt's M4A1 5.56mm Carbine |author1=Hopkins, Cameron |date=24 April 2009 |archive-url=https://web.archive.org/web/20120625060119/http://www.tactical-life.com/online/special-weapons/colts-m4a1-556mm-carbine/ |archive-date=25 June 2012 |website=Tactical-Life.com|access-date=3 April 2012|url-status=live}}</ref>

===Range and accuracy===
The M16 rifle is considered to be very accurate for a service rifle.<ref name="Newick1990">{{cite book|author=Glenn Newick |title=The Ultimate in Rifle Accuracy|url=https://books.google.com/books?id=_czqj3ORZvsC|date=October 1990|publisher=Stoeger Publishing Company|isbn=978-0-88317-159-2|pages=26–27}}</ref><ref name="Dyer2014">{{cite book|author=Lucas A. Dyer |title=A Battle Won by Handshakes|url=https://books.google.com/books?id=-Eq3AwAAQBAJ&pg=PA122|date=May 2014|publisher=iUniverse|isbn=978-1-4917-3200-7|page=122}}</ref><ref name="Halberstadt2008">{{cite book|author=Hans Halberstadt |title=Trigger Men: Shadow Team, Spider-Man, the Magnificent Bastards, and the American Combat Sniper|url=https://books.google.com/books?id=uYLh5hMBqD4C&pg=PA211|date=18 March 2008|publisher=St. Martin's Press|isbn=978-0-312-35456-5|pages=211–212}}</ref>{{Sfn|Rottman|2011|p=38}} Its light recoil, high-velocity and flat trajectory allow shooters to take headshots out to 300 meters.<ref name="autogenerated2">Sweeney, Patrick. ''Gun Digest Book of the AR-15'', Volume 2 {{page needed|date=July 2012}}</ref><ref>{{cite news |url=http://usatoday30.usatoday.com/news/world/iraq/2006-07-29-iraq-sniper_x.htm|title=Marine sniper metes out swift death in Iraq's most dangerous neighborhood|archive-url=https://web.archive.org/web/20190524151750/https://usatoday30.usatoday.com/news/world/iraq/2006-07-29-iraq-sniper_x.htm |archive-date=24 May 2019|work=USA Today |date=29 July 2006|access-date=20 November 2015|url-status=live}}</ref> Newer M16s use the newer M855 cartridge increasing their effective range to 600 meters.<ref name="Colt_Weapon_Systems" /> They are more accurate than their predecessors and are capable of shooting 1–3-inch groups at 100 yards.<ref name="alpharubicon2">[http://www.alpharubicon.com/leo/akseries.htm Avtomat Kalashnikov] {{Webarchive|url=https://web.archive.org/web/20120513012711/http://www.alpharubicon.com/leo/akseries.htm |date=13 May 2012}}. Alpharubicon.com. Retrieved on 3 April 2012.</ref><ref>Taylor, Chuck. (13 June 2009) [https://wayback.archive-it.org/all/20201201214731/https://www.tactical-life.com/firearms/in-praise-of-the-m16-rifle/?scrape=true Tactical Life. In Praise of the M16 Rifle. Why it's become the longest serving rifle in the recent US military history!] "From an accuracy standpoint, there is no comparison between the M16 and AK. As long as the upper and lower receivers are tight and the trigger is halfway decent, the M16 is capable of MOA accuracy, whereas a typical AK will produce 5 to 6 MOA at best. And, if a free-floated barrel is incorporated to the M16's design, it becomes capable of ½-MOA or better, making it fully as accurate as a finely tuned heavy-barreled bolt-action precision rifle."</ref> "In Fallujah, Iraq Marines with ACOG-equipped M16A4s created a stir by taking so many headshots that until the wounds were closely examined, some observers thought the insurgents had been executed."<ref>{{cite journal |journal=Combat Arms |title=Iraq: Lessons From The Sandbox |first=Richard |last=Venola |issn=0810-8838}}</ref> The newest M855A1 EPR cartridge is even more accurate and during testing "...has shown that, on average, 95 percent of the rounds will hit within an 8 × 8-inch (20.3 × 20.3 cm) target at 600 meters."<ref name="pica.army.mil">{{cite news |author1=Woods, Jeffrey K. LTC|issue=October–December 2010|url=http://www.pica.army.mil/picatinnypublic/news/images/highlights/2011/M855A1/32_The_Evolution_of_the_M855A1_5.56mm_Enhanced_Performance_Round,%201960-2010.pdf |website=Picatinny Arsenal |publisher=ARMY AL&T|title=The Evolution of the M855A1 5.56mm Enhanced Performance Round, 1960–2010|archive-url=https://web.archive.org/web/20130921053818/http://www.pica.army.mil/picatinnypublic/news/images/highlights/2011/M855A1/32_The_Evolution_of_the_M855A1_5.56mm_Enhanced_Performance_Round%2C%201960-2010.pdf |archive-date=21 September 2013|pages=32–35|url-status=dead}}</ref>

{| class="wikitable" style="margin: 1em auto; text-align:center;"
|- valign="top"
! rowspan="2" |Rifle
! rowspan="2" |Caliber
! rowspan="2" |Cartridge
! rowspan="2" |Cartridge <br />weight
! rowspan="2" |Bullet <br />weight
! rowspan="2" |Velocity
! rowspan="2" |Energy
! colspan="4" |Range
! colspan="2" |Accuracy
|-
! <small>Effective*</small>
! <small>Horizontal**</small>
! <small>Lethal***</small>
! <small>Maximum****</small>
! <small>10 shot group <br />@ 100 meters</small>
! <small>10 shot group <br />@ 300 meters</small>
|-
!M16
|5.56×45&nbsp;mm
|M193
|184 gr <br />(11.9 g)<ref name="krtraining1">{{cite magazine |author1=Kjellgren, G. L. M. |url=http://www.krtraining.com/KRTraining/Archive/PracticalRangeSmallArms.pdf|title=The Practical Range of Small Arms|archive-url=https://web.archive.org/web/20150305142959/http://www.krtraining.com/KRTraining/Archive/PracticalRangeSmallArms.pdf |archive-date=5 March 2015 |magazine=The American Rifleman |pages= 40–44|url-status=live}}</ref>
|55 gr <br />(3.6 g)<ref name="autogenerated2001">The Complete Encyclopedia of Automatic Army Rifles, A.E. Hartink, Hackberry Press 2001</ref>
|3,250&nbsp;fps <br />(990&nbsp;m/s)<ref name="autogenerated2001" />
|1,302&nbsp;ft/lb <br />(1,764 J)<ref name="autogenerated2001" />
|500 yds <br />(460&nbsp;m)<ref name="archive.org">{{cite web|title=Initial Adjustments - Standard Daylight Sight System|url=https://archive.org/details/OperatorsManualForM16M16a1/page/n45/mode/2up?view=theater|access-date=27 September 2011|website=Operator's Manual For M16, M16A1|pages=2–16|format=Section II}}</ref>
|711 yds <br />(650&nbsp;m)<ref name="krtraining1" />
|984 yds <br />(900&nbsp;m)<ref name="krtraining1" />
|3000 yds <br />(2700&nbsp;m)<ref name="krtraining1" />
|4.3 in <br />(11&nbsp;cm)<ref name="krtraining1" />
|}
<small>Note *: The effective range of a firearm is the maximum distance at which a weapon may be expected to be accurate and achieve the desired effect.<ref>''Dictionary of Military and Associated Terms''. US Department of Defense 2005</ref> <br />Note **: The horizontal range is the distance traveled by a bullet, fired from the rifle at a height of 1.6 meters and 0° elevation, until the bullet hits the ground.<ref>Ingalls, James Monroe (1893) ''Ballistics''. U.S. Government Printing Office. p. 7</ref> <br />Note ***: The lethal range is the maximum range of a small-arms projectile, while still maintaining the minimum energy required to put unprotected personnel out of action, which is generally believed to be 15 kilogram-meters (147&nbsp;J / 108&nbsp;ft.lbf).<ref name="krtraining1" /> This is the equivalent of the muzzle energy of a .22LR handgun.<ref>{{cite web|url=http://www.winchester.com/Products/rimfire-ammunition/Performance/super-x-rimfire/Pages/X22LRSS1.aspx |title=22 Long Rifle 40 gr. Super-X|archive-url=https://web.archive.org/web/20130203033731/http://www.winchester.com/products/rimfire-ammunition/Performance/super-x-rimfire/Pages/X22LRSS1.aspx |archive-date=3 February 2013 |website=Winchester.com|access-date=20 November 2015|url-status=dead}}</ref> <br />Note ****: The maximum range of a small-arms projectile is attained at about 30° elevation. This maximum range is only of safety interest, not for combat firing.<ref name="krtraining1" /></small>

[[File:NATO E-type Silhouette Target.PNG|thumb|upright=.5|NATO E-type Silhouette Target]]
{| class="wikitable" style="text-align: center;"
|- valign="top"
! colspan="11" |'''Single-shot hit-probability on Crouching Man (NATO E-type Silhouette) Target'''<ref name="AMSAA">{{cite web|url=http://apps.dtic.mil/dtic/tr/fulltext/u2/a228398.pdf |title=System Error Budgets, Target Distributions and Hitting Performance Estimates For General-Purpose Rifles and Sniper Rifles of 7.62 X 51 MM and Larger Calibers |website= Defense Technical Information Center |publisher=U. S. Army Material Systems Analysis Activity |author1=Weaver Jr., Jonathan M. LTC, Infantry, U. S. Army (Retired) |date=May 1990 |url-status=live |archive-url=https://web.archive.org/web/20151123093816/http://www.dtic.mil/dtic/tr/fulltext/u2/a228398.pdf|archive-date=23 November 2015}}</ref>
|-
! rowspan="2" |Rifle
! rowspan="2" |Chambering
! colspan="9" |Hit-probability <small>(With no range estimation or aiming errors)</small>
|-
! <small>50 meters</small>
! <small>100 meters</small>
! <small>200 meters</small>
! <small>300 meters</small>
! <small>400 meters</small>
! <small>500 meters</small>
! <small>600 meters</small>
! <small>700 meters</small>
! <small>800 meters</small>
|-
|M16A1 <small>(1967)</small>
|[[Engineering:5.56×45mm NATO|5.56×45&nbsp;mm NATO]] M193
|100%
|100%
|100%
|100%
|96%
|87%
|73%
|56%
|39%
|-
|M16A2 <small>(1982)</small>
|[[Engineering:5.56×45mm NATO|5.56×45&nbsp;mm NATO]] SS109/M855
|100%
|100%
|100%
|100%
|98%
|90%
|79%
|63%
|43%
|}

===Terminal ballistics===
The 5.56×45&nbsp;mm cartridge had several advantages over the 7.62×51&nbsp;mm NATO round used in the M14 rifle. It enabled each soldier to carry more ammunition and was easier to control during automatic or burst fire.<ref name="Crawford2003" /> The 5.56×45&nbsp;mm NATO cartridge can also produce massive wounding effects when the bullet impacts at high speed and yaws ("tumbles") in tissue leading to fragmentation and rapid transfer of energy.<ref>{{harvnb|Rose|2009|pp=375–376}}</ref><ref>McNab, Chris (2002). ''The SAS Training Manual'', pp. 108–109.</ref><ref>{{cite arXiv | eprint=0803.3051 | last1=Courtney | first1=Michael | last2=Courtney | first2=Amy | title=Scientific Evidence for Hydrostatic Shock | year=2008 | class=physics.med-ph }}</ref>

{| class="wikitable" style="margin: 1em auto; text-align:center;"
|- valign="top"
! rowspan="2" |Rifle
! rowspan="2" |Caliber
! rowspan="2" |Cartridge
! colspan="7" |Penetration
|-
! <small>[[Physics:Ballistic gelatin|Ballistic gelatin]] <br />@ 10 meters</small>
! <small>Sandbags <br />@ 100 meters</small>
! <small>3/4" pine boards <br />@ 100 meters</small>
! <small>Concrete building block <br />(one center rib)</small>
! <small>Steel helmet</small>
! <small>1.9mm steel <br />(14 gauge) <br />@ 100 meters</small>
! <small>4mm steel <br />(8 gauge) <br />+ layers of <br />Kevlar-29</small>
|-
!M16
|5.56×45&nbsp;mm
|M193
|<small>≈{{convert|14|in|cm|abbr=on}} <br />(bullet fragments <br />into smaller pieces)<ref name="ammo.ar15.com">{{cite web |url=https://www.ar15.com/ammo/project/Fackler_Articles/effects_of_small_arms.pdf |title=The Effects of Small Arms on the Human Body |author1= Fackler, Martin L. MD|archive-url=https://web.archive.org/web/20160607150601/http://www.ar15.com/ammo/project/Fackler_Articles/effects_of_small_arms.pdf |archive-date=7 June 2016 |access-date=27 September 2011}}</ref><ref name="autogenerated7">{{cite web |url=http://www.ciar.org/ttk/mbt/papers/misc/paper.x.small-arms.wounding-ballistics.patterns_of_military_rifle_bullets.fackler.unk.html |title=Patterns of Military Rifle Bullets |website=Ciar.org |access-date=23 August 2012 |archive-url=https://web.archive.org/web/20121120174401/http://www.ciar.org/ttk/mbt/papers/misc/paper.x.small-arms.wounding-ballistics.patterns_of_military_rifle_bullets.fackler.unk.html |archive-date=20 November 2012 |url-status=live}}</ref></small>
|<small>{{convert|4|in|cm|abbr=on}} <br />(complete bullet <br />disintegration)<ref name="RES">{{cite web |url=https://apps.dtic.mil/sti/pdfs/ADA050268.pdf |title=Rifle Evaluation Study |archive-url=https://web.archive.org/web/20121201205751/http://www.dtic.mil/cgi-bin/GetTRDoc?Location=U2&doc=GetTRDoc.pdf&AD=ADA050268 |archive-date=1 December 2012 |website= U.S. Army, Infantry Combat Developments Agency |url-status=live |date=17 February 1978}}</ref></small>
|<small>8 boards <br />(bullet tumbled)<ref name="RES" /></small>
|<small>one side to 200&nbsp;m<ref name="RES" /></small>
|<small>both sides to 300&nbsp;m <br />one side to 500&nbsp;m<ref name="RES" /></small>
|<small>2 layers<ref name="RES" /></small>
|<small>31 layers of Kevlar<ref name="bgu">{{cite web |author1=Slepyan, L.I. |author2=Ayzenberg-Stepanenko, M.V. |url=http://www.cs.bgu.ac.il/~ayzenbe/44_1998.pdf |title=PENETRATION OF METAL-FABRICS COMPOSITES BY SMALL PROJECTILES |archive-url=https://web.archive.org/web/20151107045834/http://www.cs.bgu.ac.il/~ayzenbe/44_1998.pdf |archive-date=7 November 2015 |website=Personal Armour Systems |publisher=British Crown Copyright/MOD The Institute for Industrial Mathematics |date=1998}}</ref></small>
|}

{{multiple image
| caption_align = center
| header_align = center
| align = right
| direction = vertical
| width = 300
| header = [[Physics:Wound ballistics|Wound profiles]] in ballistic gelatin <br /><small>Note: images are not to same scale</small>
| image1 = M16 5.56x45mm wound ballistics.gif
| alt1 = M16 5.56×45mm wound ballistics
| caption1 = M16 M193 5.56×45&nbsp;mm
| image2 = M16A2 M855 5.56X45mm NATO wound ballistics.gif
| alt2 = M16A2 M855 5.56×45mm wound ballistics
| caption2 = M16A2 SS109/M855 5.56×45&nbsp;mm NATO
}}

The original ammunition for the M16 was the 55-grain M193 cartridge. When fired from a {{cvt|20|in|mm}} barrel at ranges of up to {{convert|100|m|ft|sigfig=1|order=flip}}, the thin-jacketed lead-cored round traveled fast enough (above {{cvt|2900|ft/s|m/s}}) that the force of striking a human body would cause the round to yaw (or tumble) and fragment into about a dozen pieces of various sizes thus created wounds that were out of proportion to its caliber.<ref name="ammo.ar15.com" /><ref name="autogenerated7" /> These wounds were so devastating that many considered the M16 to be an inhumane weapon.<ref name="m1-18">{{cite web |author1=Parks, W. Hays |url=http://www.dtic.mil/ndia/2010armament/TuesdayLandmarkBHaysParks.pdf |title=International Legal Initiatives to Restrict Military Small Arms Ammunition |archive-url=https://web.archive.org/web/20111129211606/http://www.dtic.mil/ndia/2010armament/TuesdayLandmarkBHaysParks.pdf |archive-date=29 November 2011 |date=2010|website=Defense Technical Information Center (DTIC)|publisher=International Committee of the Red Cross (ICRC)|pages=1–18|url-status=dead |quote=Those who consider the M16 inhumane include; the International Committee of the Red Cross, Austria, Argentina, Belgium, Bolivia, Bulgaria, Burundi, Cambodia, Cyprus, Germany, Ireland, Latvia, Lithuania, Luxembourg, Mauritius, Mexico, Romania, Samoa, Slovenia, Sweden, Switzerland, etc.}}</ref><ref>{{cite book |author1=Ian V. Hogg |author2=John S. Weeks |title=Military Small Arms of the 20th Century |url=https://books.google.com/books?id=teAAHt1GaE8C |access-date=27 September 2011|year=2000|publisher=Krause Publications|isbn=978-0-87341-824-9|archive-url=https://web.archive.org/web/20140103132510/http://books.google.com/books?id=teAAHt1GaE8C|archive-date=3 January 2014 |url-status=live}}</ref><ref>{{cite web |url=http://www.icrc.org/eng/resources/documents/misc/57jmma.htm |title=The Swiss draft Protocol on Small-Calibre Weapon Systems |date=31 August 1995 |publisher=International Review of the Red Cross |issue=307 |author1=Prokosch, Eric |archive-url=https://web.archive.org/web/20150707194426/https://www.icrc.org/eng/resources/documents/misc/57jmma.htm |archive-date=7 July 2015 |website=Icrc.org |access-date=20 November 2015}}</ref> As the 5.56&nbsp;mm round's velocity decreases, so does the number of fragments that it produces.<ref name="ReferenceA" /> The 5.56&nbsp;mm round does not normally fragment at distances beyond 200 meters or at velocities below 2500&nbsp;ft/s, and its lethality becomes largely dependent on shot placement.<ref name="ReferenceA" /><ref name="autogenerated7" />

With the development of the M16A2, the new 62-grain M855 cartridge was adopted in 1983. The heavier bullet had more energy and was made with a steel core to penetrate Soviet [[Engineering:Body armor|body armor]]. However, this caused less fragmentation on impact and reduced effects against targets without armor, both of which lessened kinetic energy transfer and wounding ability.<ref name="Reliable" /> Some soldiers and Marines coped with this through training, with requirements to shoot vital areas three times to guarantee killing the target.<ref>{{cite web |url=http://atwar.blogs.nytimes.com/2009/11/03/the-m-16-argument-heats-up-again/ |title=The M-16 Argument Heats Up, Again |archive-url=https://web.archive.org/web/20130616080901/http://atwar.blogs.nytimes.com/2009/11/03/the-m-16-argument-heats-up-again/ |archive-date=16 June 2013 |work=The New York Times |date=3 November 2009}}</ref>

However, there have been repeated and consistent reports of the M855's inability to wound effectively (i.e., fragment) when fired from the short barreled M4 carbine (even at close ranges).<ref name="ReferenceA" /> The M4's 14.5-in. barrel length reduces muzzle velocity to about 2900&nbsp;ft/s.<ref name="M4_Colt_Specs">{{cite web |url=http://www.colt.com/mil/M4_2.asp |title=M4 5.56mm Carbine |website=Colt.com |archive-url=https://web.archive.org/web/20110616210348/http://www.colt.com/mil/M4_2.asp|archive-date=16 June 2011 |access-date=8 October 2011}}</ref> This reduced wounding ability is one reason that, despite the Army's transition to short-barrel M4s, the Marine Corps has decided to continue using the M16A4 with its 20-inch barrel as the 5.56×45&nbsp;mm M855 is largely dependent upon high velocity in order to wound effectively.<ref name="ReferenceA" />

In 2003, the U.S. Army contended that the lack of lethality of the 5.56×45&nbsp;mm was more a matter of perception than fact.<ref name="militec2">{{cite web |url=http://militec1.com/swat.pdf |title=Project manager soldier weapons assessment team report 6-03 |archive-url=https://web.archive.org/web/20110714094113/http://militec1.com/swat.pdf |archive-date=14 July 2011|access-date=8 October 2011}}</ref><ref>{{cite journal |last1= Dean |first1= Glenn |last2= LaFontaine |first2= David |title= Small Caliber Lethality: 5.56 Performance in Close Quarters Battle |url= http://wstiac.alionscience.com/pdf/WQV8N1_ART01.pdf |journal= WSTIAC Quarterly |volume= 8 |issue= 1 |page= 3 |url-status= dead |archive-url= https://web.archive.org/web/20120212205748/http://wstiac.alionscience.com/pdf/WQV8N1_ART01.pdf |archive-date= 12 February 2012}}</ref> With good shot placement to the head and chest, the target was usually defeated without issue.<ref name="militec2" /><ref>{{cite journal |url=http://sadefensejournal.com/wp/?p=769 |title=Is there a Problem with the Lethality of the 5.56 NATO Caliber? |author1=Arvidsson, Per |date=6 January 2012 |archive-url=https://web.archive.org/web/20131012052014/http://sadefensejournal.com/wp/?p=769 |archive-date=12 October 2013 |journal=Small Arms Defense Journal |access-date=20 November 2015}}</ref> The majority of failures were the result of hitting the target in non-vital areas such as extremities.<ref name="militec2" /> However, a minority of failures occurred in spite of multiple hits to the chest.<ref name="militec2" /> In 2006, a study found that 20% of soldiers using the M4 Carbine wanted more lethality or stopping power.<ref name="american_rifle">{{cite book|last=Rose|first=Alexander |title=American Rifle: A Biography|year=2009|publisher=Delta|isbn=978-0-553-38438-3|pages=403–405}}</ref> In June 2010, the U.S. Army announced it began shipping its new 5.56&nbsp;mm, lead-free, M855A1 Enhanced Performance Round to active combat zones.<ref name="autogenerated4">{{cite web |url=http://www.army.mil/article/48657/ |title=Evolution of the M855A1 Enhanced Performance Round |publisher=The United States Army |archive-url=https://web.archive.org/web/20140420171100/http://www.army.mil/article/48657 |archive-date=20 April 2014 |website=U.S. Army |access-date=19 November 2011}}</ref> This upgrade is designed to maximize performance of the 5.56×45&nbsp;mm round, to extend range, improve accuracy, increase penetration and to consistently fragment in soft-tissue when fired from not only standard length M16s, but also the short-barreled M4 carbines.<ref name="pica.army.mil" /><ref name="autogenerated4" /><ref>{{cite web |url=http://www.gpo.gov/fdsys/pkg/CHRG-111shrg64544/pdf/CHRG-111shrg64544.pdf |title=The current readiness of the U.S. forces: hearing before the Subcommittee on Readiness and Management Support of the Committee on Armed Services, United States Senate, One Hundred Eleventh Congress, second session, April 14, 2010|format=S. HRG. 111–868|archive-url=https://web.archive.org/web/20170310170921/https://www.gpo.gov/fdsys/pkg/CHRG-111shrg64544/pdf/CHRG-111shrg64544.pdf |archive-date=10 March 2017 |date=14 April 2010 |publisher=U.S. Government Printing Office|location=Washington}}</ref> The U.S. Army has been impressed with the new M855A1 EPR round.<ref>{{cite web |author1=Slowik, Max |date=6 September 2012 |url=http://www.guns.com/2012/09/06/new-m855a1-epr-enhanced-performance-round-camp-perry-101-abn-video/ |title= New M855A1 Enhanced Performance Round smashing expectations |archive-url=https://web.archive.org/web/20131203022449/http://www.guns.com/2012/09/06/new-m855a1-epr-enhanced-performance-round-camp-perry-101-abn-video/ |archive-date=3 December 2013}}</ref> A 7.62 NATO M80A1 EPR variant was also developed.<ref>{{cite web |url=https://www.thefirearmblog.com/blog/2016/06/16/wound-channel-tests-7-62-308-m80a1-epr-glorious/ |archive-url=https://web.archive.org/web/20181022033658/https://www.thefirearmblog.com/blog/2016/06/16/wound-channel-tests-7-62-308-m80a1-epr-glorious/ |archive-date=22 October 2018 |title=DEVASTATING New M80A1 7.62mm Round|website=TheFirearmBlog|date=16 June 2016 }}</ref><ref>{{cite web |url=https://www.thefirearmblog.com/blog/2016/07/23/taking-a-look-inside-the-armys-devastating-new-m80a1-7-62mm-round/|archive-url=https://web.archive.org/web/20181022033553/https://www.thefirearmblog.com/blog/2016/07/23/taking-a-look-inside-the-armys-devastating-new-m80a1-7-62mm-round/ |archive-date=22 October 2018 |title=Taking a Look Inside the Army's DEVASTATING New M80A1 7.62mm Round|website=TheFirearmBlog|date=23 July 2016 }}</ref>

===Magazines===
[[File:Stanag mags.jpg|thumb|right|Vietnam War-era 20-round magazine (left) and current issue NATO STANAG 30-round magazine (right)]]
[[File:Improved M16 Magazine Follower.jpg|thumb|Improved tan colored M16 magazine follower]]

The M16's magazine was meant to be a lightweight, disposable item.<ref name="americanrifleman1">{{cite web |last=Bartocci |first=Christopher R. |url=http://www.americanrifleman.org/ArticlePage.aspx?id=2157&cid=4 |title=Feeding the Modern Semi-Automatic Rifle |publisher=Americanrifleman.org |date=20 July 2011 |access-date=23 August 2012 |archive-url=https://web.archive.org/web/20130414211200/http://www.americanrifleman.org/ArticlePage.aspx?id=2157&cid=4 |archive-date=14 April 2013 |url-status=dead}}</ref> As such, it is made of pressed/stamped aluminum and was not designed to be durable.<ref name="autogenerated6">{{cite web |author1=Ehrhart, Thomas P. |url=https://apps.dtic.mil/sti/pdfs/ADA512331.pdf|title=Increasing Small Arms Lethality in Afghanistan: Taking Back the Infantry Half-Kilometer|archive-url=https://web.archive.org/web/20130906131406/http://www.dtic.mil/cgi-bin/GetTRDoc?AD=ADA512331 |archive-date=6 September 2013 |website=School of Advanced Military Studies |publisher=United States Army Command and General Staff College|location=Fort Leavenworth, Kansas|date=2009 |url-status=live}}</ref> The M16 originally used a 20-round magazine which was later replaced by a bent 30-round design. As a result, the magazine follower tends to rock or tilt, causing malfunctions.<ref name="americanrifleman1" /> Many non-U.S. and commercial magazines have been developed to effectively mitigate these shortcomings (e.g., H&K's all-stainless-steel magazine, Magpul's polymer P-MAG, etc.).<ref name="autogenerated6" /><ref name="americanrifleman1" />

Production of the 30-round magazine started late 1967 but did not fully replace the 20-round magazine until the mid-1970s.<ref name="americanrifleman1" /> Standard USGI aluminum 30-round M16 magazines weigh {{convert|0.11|kg|lb|abbr=on|order=flip}} empty and are {{convert|7.1|in|cm|abbr=out}} long.<ref name="M4_Colt_Specs" /><ref name="Crane_SurFire">{{cite web |author1=Crane, David |url=http://www.defensereview.com/dr-exclusive-surefire-60-shot-and-100-shot-ar-ar-15m16-5-56mm-nato-box-magazines-for-infantry-combat-and-tactical-engagements-meet-the-surefire-mag5-60-and-mag5-100-high-capacity-magazines-hcms/|title=SureFire "Quad-Stack" AR Rifle Magazines: SureFire 60-Shot and 100-Shot AR (AR-15/M16) 5.56mm NATO Box Magazines for Significantly-Increased Firepower during Infantry Combat and Tactical Engagements of All Sorts: Meet the SureFire MAG5-60 and MAG5-100 High Capacity Magazines (HCMs)"Quad-Stack" AR Rifle Magazines: 60-Round/Shot and 100-Round/Shot AR (AR-15/M16) 5.56mm NATO Box Magazines for Significantly-Increased Firepower during Infantry Combat and Tactical Engagements of All Sorts|archive-url=https://web.archive.org/web/20150321042519/http://www.defensereview.com/dr-exclusive-surefire-60-shot-and-100-shot-ar-ar-15m16-5-56mm-nato-box-magazines-for-infantry-combat-and-tactical-engagements-meet-the-surefire-mag5-60-and-mag5-100-high-capacity-magazines-hcms/ |archive-date=21 March 2015 |website=Defense Review|date=3 December 2010|quote=Standard MILSPEC USGI 30-Round Magazine Specs (data provided by SureFire): Height: 7.1" and Weight-Empty: 3.9 ounces|url-status=live}}</ref> The newer plastic magazines are about a half-inch longer.<ref>{{cite web|author1=Crane, David|url=http://www.defensereview.com/lancer-systems-l5-translucent-polymer-30-round-magazine-for-tactical-ars/ |title=Lancer Systems L5 Translucent Polymer 30-Round Magazine for Tactical ARs] |archive-url=https://web.archive.org/web/20180703142848/http://www.defensereview.com/lancer-systems-l5-translucent-polymer-30-round-magazine-for-tactical-ars/ |archive-date=3 July 2018|website=Defense Review |date=23 January 2009|url-status=live}}</ref> The newer steel magazines are about 0.5-inch longer and four ounces heavier.<ref>{{cite web |url=https://www.scribd.com/doc/97921277/Heckler-Koch-HK416-Enhanced-Carbine-556x45mm-NATO |title=Heckler Koch HK416 Enhanced Carbine 556x45mm NATO |access-date=9 September 2017 |url-status=dead |archive-url=https://web.archive.org/web/20131203013936/http://www.scribd.com/doc/97921277/Heckler-Koch-HK416-Enhanced-Carbine-556x45mm-NATO |archive-date=3 December 2013}} |HK high-reliability 30-round steel magazine fact sheet</ref> The M16's magazine has become the unofficial NATO [[Engineering:STANAG magazine|STANAG magazine]] and is currently used by many Western nations, in numerous weapon systems.{{Sfn|Rottman|2011|pp=35-36}}<ref>Future Weapons, Kevin Dockery, Penguin, 2007, pp. 125-126.</ref>

In 2009, the U.S. Military began fielding an "improved magazine" identified by a tan-colored follower.<ref>{{cite magazine |url=http://peosoldier.armylive.dodlive.mil/2009/12/14/armys-improved-magazine-increases-weapons-reliability-%e2%80%9ctan-is-the-plan%e2%80%9d-for-the-new-magazine/|title=Article includes a magazine animation|archive-url=https://web.archive.org/web/20130224100200/http://peosoldier.armylive.dodlive.mil/2009/12/14/armys-improved-magazine-increases-weapons-reliability-%e2%80%9ctan-is-the-plan%e2%80%9d-for-the-new-magazine/ |archive-date=24 February 2013 |magazine=Peo Soldier Live |date=14 December 2009 |access-date=24 December 2011|url-status=dead}}</ref><ref name="army.mil">{{cite web |url=http://www.army.mil/article/31880/ |title=Improved magazine increases weapons reliability |publisher=The United States Army|archive-url=https://web.archive.org/web/20130922143649/http://www.army.mil/article/31880/ |archive-date=22 September 2013 |website=Picatinny Arsenal|author1=PEO Soldier|url-status=live |access-date=24 December 2011}}</ref> "The new follower incorporates an extended rear leg and modified bullet protrusion for improved round stacking and orientation. The self-leveling/anti-tilt follower minimizes jamming while a wider spring coil profile creates even force distribution. The performance gains have not added weight or cost to the magazines."<ref name="army.mil" />

In July 2016, the U.S. Army introduced another improvement, the new Enhanced Performance Magazine, which it says will result in a 300% increase in reliability in the M4 Carbine. Developed by the United States Army Armament Research, Development and Engineering Center and the Army Research Laboratory in 2013, it is tan colored with blue follower to distinguish it from earlier, incompatible magazines.<ref>{{cite news|publisher=Soldier Systems Daily|title=First Look – New US Army 30 Round Enhanced Performance Magazine for M4A1|url=http://soldiersystems.net/2016/08/16/first-look-new-us-army-enhanced-performance-magazine-for-m4a1|date=8 August 2016|access-date=31 August 2016|archive-url=https://web.archive.org/web/20160907033235/http://soldiersystems.net/2016/08/16/first-look-new-us-army-enhanced-performance-magazine-for-m4a1/|archive-date=7 September 2016|url-status=live}}</ref>

===Muzzle devices===
Most M16 rifles have a barrel threaded in 1⁄2-28" threads to incorporate the use of a muzzle device such as a flash suppressor or sound suppressor.<ref name="Sweeney2012">{{cite book|last=Sweeney|first=Patrick |title=Gun Digest Book of the AR-15|year=2012|publisher=Gun Digest Books|location=Iola, Wisconsin|isbn=978-1-4402-2868-1|page=67}}</ref> The initial flash suppressor design had three tines or prongs and was designed to preserve the shooter's night vision by disrupting the flash. Unfortunately it was prone to breakage and getting entangled in vegetation. The design was later changed to close the end to avoid this and became known as the "A1" or "bird cage" flash suppressor on the M16A1. Eventually on the M16A2 version of the rifle, the bottom port was closed to reduce muzzle climb and prevent dust from rising when the rifle was fired in the prone position.<ref name="Wieland2011">{{cite book|last=Wieland|first=Terry |title=Gun Digest Book of Classic American Combat Rifles|date=22 November 2011|publisher=Krause Publications|location=Iola, Wisconsin|isbn=978-1-4402-3017-2|page=100}}</ref> For these reasons, the U.S. military declared the A2 flash suppressor as a compensator or a muzzle brake; but it is more commonly known as the "GI" or "A2" flash suppressor.<ref name="Crawford2003">{{cite book|author=Steve Crawford |title=Twenty First Century Small Arms: The World's Great Infantry Weapons|url=https://books.google.com/books?id=z7nW8LpDOBoC&pg=PA85|access-date=6 June 2013|year=2003|publisher=Zenith Imprint|isbn=978-0-7603-1503-3|pages=85–86}}</ref>

The M16's [[Engineering:Vortex Flash Hider|Vortex Flash Hider]] weighs 3 ounces, is 2.25 inches long, and does not require a lock washer to attach to the barrel.<ref name="swat">{{cite journal |last=Hansen |first=Denny |pages =28–32 |title=Flash Hiders, is there a difference? |journal=SWAT |year=2005 |issue=2 |volume=24}}</ref> It was developed in 1984 and is one of the earliest privately designed muzzle devices. The U.S. military uses the Vortex Flash Hider on M4 carbines and M16 rifles.<ref>NATO Stock Number of NSN 1005-01-591-5825, PN 1001V</ref><ref>{{cite web|url=http://www.armyproperty.com/nsn/1005-01-591-5825|title=NSN 1005-01-591-5825|access-date=6 June 2013|archive-url=https://web.archive.org/web/20130922070108/http://www.armyproperty.com/nsn/1005-01-591-5825|archive-date=22 September 2013|url-status=live}}</ref> A version of the Vortex has been adopted by the Canadian Military for the Colt Canada C8 CQB rifle.<ref>{{cite web|url=http://www.coltcanada.com/products-c8iur.htm |title=Colt Canada Corporation |year=212 |access-date=6 June 2013 |url-status=dead |archive-url=https://web.archive.org/web/20130922063015/http://www.coltcanada.com/products-c8iur.htm |archive-date=22 September 2013}}</ref> Other flash suppressors developed for the M16 include the Phantom Flash Suppressor by Yankee Hill Machine (YHM) and the KX-3 by Noveske Rifleworks.<ref name="SweeneyARBOOK">{{cite book|last=Sweeney|first=Patrick |title=The Gun Digest Book of The AR-15|chapter-url=https://books.google.com/books?id=ywqWgSSn2KIC&pg=PA255|access-date=6 June 2013|date=11 August 2010|publisher=Gun Digest Books|location=Iola, Wisconsin|isbn=978-1-4402-1622-0|pages=255–256|chapter=21}}</ref>

The threaded barrel allows sound suppressors with the same thread pattern to be installed directly to the barrel; however this can result in complications such as being unable to remove the suppressor from the barrel due to repeated firing on full auto or three-round burst.<ref name="Walker2012">{{cite book|last=Walker|first=Robert E. |title=Cartridges and Firearm Identification|year=2012|publisher=CRC Press|location=Florence, KY|isbn=978-1-4665-0206-2|page=295}}</ref> A number of suppressor manufacturers have designed "direct-connect" sound suppressors which can be installed over an existing M16's flash suppressor as opposed to using the barrel's threads.<ref name="Walker2012" />

===Grenade launchers and shotguns===
[[File:Loading M203 40 mm grenade launcher attached to an M16 rifle.jpg|right|thumb|Loading an M203 40&nbsp;mm grenade launcher attached to an M16A1 rifle with a practice round]]

All current M16-type rifles can mount under-barrel 40&nbsp;mm grenade launchers, such as the M203 and [[Engineering:M320 Grenade Launcher Module|M320]]. Both use the same [[Engineering:40 mm grenade#40×46 mm LV (40 mm Low Velocity)|40×46mm LV]] grenades as the older, stand-alone [[Engineering:M79 grenade launcher|M79 grenade launcher]]. The M16 can also mount under-barrel 12 gauge shotguns such as KAC Masterkey or the M26 Modular Accessory Shotgun System.

===Riot Control Launcher===
[[File:M234.png|thumb|upright=1.3|left|M234 Riot Control Launcher]]
The [[Engineering:M234 launcher|M234 Riot Control Launcher]] is an M16-series rifle attachment firing an [[Engineering:5.56×45mm NATO#Military cartridges|M755 blank round]]. The M234 mounts on the muzzle, bayonet lug, and front sight post of the M16. It fires either the M734 64&nbsp;mm Kinetic Riot Control or the M742 64&nbsp;mm CSI Riot Control Ring Airfoil Projectiles. The latter produces a 4 to 5-foot [[Chemistry:Tear gas|tear gas]] cloud on impact. The main advantage to using Ring Airfoil Projectiles is that their design does not allow them to be thrown back by rioters with any real effect. The M234 is no longer used by U.S. forces. It has been replaced by the M203 grenade launcher and nonlethal ammunition.

===Bayonet===
The M16 is {{convert|44.25|in|mm}} long with an M7 bayonet attached.<ref name="archive.org" /> The M7 bayonet is based on earlier designs such as the M4, M5, & M6 bayonets, all of which are direct descendants of the M3 Fighting Knife and have spear-point blade with a half sharpened secondary edge. The newer M9 bayonet has a clip-point blade with saw teeth along the spine and can be used as a multi-purpose knife and wire-cutter when combined with its scabbard. The current USMC OKC-3S bayonet bears a resemblance to the Marines' iconic Ka-Bar fighting knife with serrations near the handle.

===Bipod===
For use as an ad-hoc automatic rifle, the M16 and M16A1 could be equipped with the XM3 bipod, later standardized as the ''Bipod, M3'' (1966)<ref>RIFLE, 5.56-MM, XM16E1. Headquarters, Department of the Army, 12 July 1966 p.4</ref> and ''Rifle Bipod M3'' (1983).<ref>Technical Manual: Organizational, Direct Support, and General Support Maintenance Manual (Including Repair Parts and Special Tools List): Rifle, 5.56-mm, M16 (1005-00-856-6885): Rifle, 5.56-mm, M16A1 (1005-00-073-9421). Headquarters, Department of the Army. 25 November 1983 p. 1-3</ref> Weighing only 0.6&nbsp;lb, the simple and non-adjustable bipod clamps to the barrel of the rifle to allow for supported fire.

The M3 bipod continues to be referenced in at least one official manual as late as 1985, where it is stated that one of the most stable firing positions is "the prone biped [sic] supported for automatic fire."<ref>The Mechanized Infantry Platoon and Squad (APC). Headquarters, Department of the Army. March 1985. p. B-1</ref>

==NATO standards==
In March 1970, the U.S. recommended that all NATO forces adopt the 5.56×45&nbsp;mm cartridge.<ref name="autogenerated3" /> This shift represented a change in the philosophy of the military's long-held position about caliber size. By the mid 1970s, other armies were looking at M16-style weapons. A NATO standardization effort soon started and tests of various rounds were carried out starting in 1977.<ref name="autogenerated3" /> The U.S. offered the 5.56×45&nbsp;mm M193 round, but there were concerns about its penetration in the face of the wider introduction of body armor.<ref name="ReferenceA" /> In the end the Belgian 5.56×45&nbsp;mm SS109 round was chosen (STANAG 4172) in October 1980.<ref name="autogenerated3" /> The SS109 round was based on the U.S. cartridge but included a new stronger, heavier, 62 grain bullet design, with better long range performance and improved penetration (specifically, to consistently penetrate the side of a steel helmet at 600 meters).<ref name="ReferenceA" /> Due to its design and lower muzzle velocity (about 3110&nbsp;ft/s)<ref name="archivemil">{{cite web |url=http://www.colt.com/mil/M16_2.asp|archive-url=https://web.archive.org/web/20110616211557/http://www.colt.com/mil/M16_2.asp|archive-date=16 June 2011 |title= M16 5.56mm Rifle|website=Colt.com|access-date=8 October 2011|url-status=dead}}</ref> the Belgian SS109 round is considered more humane because it is less likely to fragment than the U.S. M193 round.<ref name="m1-18" /> The NATO 5.56×45&nbsp;mm standard ammunition produced for U.S. forces is designated M855.

In October 1980, shortly after NATO accepted the 5.56×45&nbsp;mm NATO rifle cartridge.<ref>{{cite web |author1=Watters, Daniel |url=http://www.thegunzone.com/556dw-8.html |title=The 5.56 X 45mm Timeline: A Chronology of Development|archive-url=https://web.archive.org/web/20150316235202/http://thegunzone.com/556dw-8.html |archive-date=16 March 2015 |website=The Gun Zone|publisher=2000–2007}}</ref> Draft Standardization Agreement 4179 (STANAG 4179) was proposed to allow NATO members to easily share rifle [[Engineering:Ammunition|ammunition]] and magazines down to the individual soldier level. The magazine chosen to become the ''STANAG magazine'' was originally designed for the U.S. M16 rifle. Many NATO member nations, but not all, subsequently developed or purchased rifles with the ability to accept this type of magazine. However, the standard was never ratified and remains a 'Draft STANAG'.<ref>{{cite web|url=http://www.dtic.mil/ndia/2008Intl/Arvidsson.pdf|title=NATO Infantry Weapons Standardization |archive-url=https://web.archive.org/web/20121201183951/http://www.dtic.mil/ndia/2008Intl/Arvidsson.pdf |archive-date=1 December 2012|website=NDIA Conference |url-status=dead|date=2008}}</ref>

All current M16 type rifles are designed to fire STANAG [[Engineering:22 mm grenade|22&nbsp;mm]] [[Engineering:Rifle grenade|rifle grenade]]s from their integral flash hiders without the use of an adapter. These 22&nbsp;mm grenade types range from anti-tank rounds to simple finned tubes with a fragmentation hand grenade attached to the end. They come in the "standard" type which are propelled by a blank cartridge inserted into the chamber of the rifle. They also come in the "bullet trap" and "shoot through" types, as their names imply, they use live ammunition. The U.S. military does not generally use rifle grenades; however, they are used by other nations.<ref>{{cite web |url=http://www.mecar.be/content.php?langue=english&cle_menus=1156765282 |title=Mecar rifle grenades |publisher=Mecar.be |date=28 August 2006 |access-date=13 July 2014 |archive-url=https://web.archive.org/web/20140318031954/http://www.mecar.be/content.php?langue=english&cle_menus=1156765282 |archive-date=18 March 2014 |url-status=dead}}</ref>

The [[Engineering:NATO Accessory Rail|NATO Accessory Rail]] STANAG 4694, or Picatinny rail STANAG 2324, or a "Tactical Rail" is a bracket used on M16 type rifles to provide a standardized mounting platform. The rail comprises a series of ridges with a T-shaped cross-section interspersed with flat "spacing slots". Scopes are mounted either by sliding them on from one end or the other; by means of a "rail-grabber" which is clamped to the rail with bolts, thumbscrews or levers; or onto the slots between the raised sections. The rail was originally for scopes. However, once established, the use of the system was expanded to other accessories, such as tactical lights, laser aiming modules, night vision devices, reflex sights, foregrips, bipods, and bayonets.

Currently, the M16 is in use by 15 NATO countries and more than 80 countries worldwide.

==Variants==

===M16===
[[File:Armamento - Museo de Armas de la Nación 05.JPG|thumb|An early M16 rifle without forward-assist. Note: "duckbill" flash suppressor and triangular handguard]]

This was the first M16 variant adopted operationally, originally by the U.S. Air Force. It was equipped with triangular handguards, buttstocks without a compartment for the storage of a cleaning kit,<ref name="SAOW2" /> a three-pronged "duckbill" flash suppressor designed to preserve the shooter's night vision by disrupting the flash, full auto, and no forward assist. The M16 has a safe/semi/auto selective fire trigger group. Bolt carriers were originally chrome plated and slick-sided, lacking forward assist notches. Later, the chrome-plated carriers were dropped in favor of Army-issued notched and parkerized carriers, though the interior portion of the bolt carrier is still chrome-lined. The barrel rifling had a 1:12 (305&nbsp;mm) [[Engineering:Rifling#Twist rate|twist rate]] to adequately stabilize the M193 ball and M196 tracer ammunition. The Air Force continued to operate these weapons until around 2001, at which time the Air Force converted all of its M16s to the M16A2 configuration.

The M16 was also adopted by the British SAS, who used it during the Falklands War.<ref name="special_operations1">{{cite web |url=http://www.specialoperations.com/Foreign/United_Kingdom/SAS/Weapons.htm |title=SAS Weapons |archive-url=https://web.archive.org/web/20080712082335/http://www.specialoperations.com/Foreign/United_Kingdom/SAS/Weapons.htm |archive-date=12 July 2008|website=Special Operations.Com|date=2000|location=United Kingdom|url-status=dead}}</ref>

===XM16E1 and M16A1 (Colt Model 603)===
[[File:NARA 111-CCV-349-CC43120 101st Airborne soldiers firing XM148 Operation Cook 1967.jpg|thumb|XM16E1 with [[Engineering:XM148 grenade launcher|XM148 grenade launcher]]]]
[[File:M16A1 brimob.jpg|thumb|M16A1 rifle with 30-round magazine]]

The U.S. Army XM16E1 was essentially the same weapon as the M16 with the addition of a forward assist and corresponding notches in the chrome bolt carrier, and even included the addition of three-pronged flash hiders. The M16A1 was the finalized production model in 1967 and was produced until 1982.

To address issues raised by the XM16E1's testing cycle, a closed, birdcage symmetric flash suppressor with open side slots to the top, bottom, left and right replaced the XM16E1's three-pronged flash suppressor which caught on twigs and leaves from 1967 onwards.<ref>{{Cite web|url=https://retrorifles.com/m16a1-birdcage-flash-hiders/|title=M16A1 Birdcage Flash Hiders|website=Retro Rifles}}</ref> Various other changes were made after numerous problems in the field. Cleaning kits were developed and issued, while barrels with chrome-plated chambers and later fully lined bores were introduced. A small storage compartment inside the stock was introduced.<ref>{{cite web |url=https://archive.org/details/OperatorsManualForM16M16a1/page/n141/mode/2up?view=theater |website=Operator's Manual For M16, M16A1|title= E2-E3 Buttstock storage |format=Section II |pages=E2–E3|access-date=8 October 2011}}</ref> The buttstock storage compartment is often used for storing a basic cleaning kit. To promote reliability and durability, the mechanical behavior of the operating system was revised to make it compatible for using US military issued ammunition loaded with WC846 ball powder (which reaches peak pressure significantly quicker than the extruded IMR8208M powder and increases the cyclic rate of fire for which the operating system was originally designed). Revisions like reducing the diameter of the gas port to mitigate the higher port pressure caused by the ball powder to properly gas the operating system again, updating the buffer assembly, changing the bolt carrier surface finish to manganese phosphate and the gas tube material to stainless steel contributed to improved mechanical behavior.

With these and other changes, the malfunction rate slowly declined, and new soldiers were generally unfamiliar with early problems. A rib was built into the side of the receiver on the XM16E1 to help prevent accidentally pressing the magazine release button while closing the ejection port cover. This rib was later extended on production M16A1s to help in preventing the magazine release from inadvertently being pressed. The hole in the bolt that accepts the cam pin was crimped inward on one side, in such a way that the cam pin may not be inserted with the bolt installed backwards, which would cause failures to eject until corrected. The M16A1 saw limited use in training capacities until the early 2000s,<ref>{{cite web|url=http://www.defense.gov/Photos/newsphoto.aspx?newsphotoid=2931 |title=Defense.gov Photos : News Photo|date=1 March 2010|website=Defense.gov|url-status=dead |archive-url=https://web.archive.org/web/20100301153228/http://www.defense.gov/Photos/newsphoto.aspx?newsphotoid=2931|archive-date=1 March 2010}}</ref><ref>{{cite web|url=http://www.defense.gov/photos/Jul2000/000716-F-6217S-015.html |title=Sgt. Zachary Sarver and Spc. Gary Vandenbos negotiate with a role-playing inebriated woodsman during Exercise Peaceshield 2000.|date=2000|access-date=9 November 2004|website=Defense.gov|url-status=dead |archive-url=https://web.archive.org/web/20041109092325/http://www.defense.gov/photos/Jul2000/000716-F-6217S-015.html|archive-date=9 November 2004}}</ref><ref>{{cite web|url=http://www.navy.mil/view_image.asp?id=9872 |title=Navy.mil – View Image|date=29 December 2017|website=Navy.mil|url-status=live |archive-url=https://web.archive.org/web/20171229124113/http://www.navy.mil/view_image.asp?id=9872|archive-date=29 December 2017}}</ref> but is no longer in active service with the U.S., although is still standard issue in many world armies.

===M16A2===
[[File:Capt. John Arthur tackles the stress shoot event (7646423312).jpg|thumb|Spent case being deflected after firing an M16A2 (Model 705 with Safe/Semi/Burst trigger group) by a left-handed user]]
[[File:M16A2 Enhanced with a complete trigger group.jpg|thumb|M16A2 Enhanced rifle (Model 708 with Safe/Semi/Burst/Auto trigger group)]]
[[File:M16a2m203 afmil.jpg|thumb|M16A2 with a heat shield hand guard and an M203 grenade launcher under it]]

The development of the M16A2 rifle was originally requested by the United States Marine Corps in 1979 as a result of combat experience in Vietnam with the M16A1.<ref>{{Cite book |last1=Clinton Ezell |first1=Edward |title=The Black Rifle: M16 Retrospective |last2=Blake Stevens |first2=Robert |publisher=Collector Grade Publications |year=1992 |pages=343}}</ref> It was officially adopted by the Department of Defense as the "Rifle, 5.56&nbsp;mm, M16A2" in 1983.{{Sfn|Rottman|2011|p=36}} The Marines were the first branch of the U.S. Armed Forces to adopt it, in the early/mid-1980s, with the United States Army following suit in 1986.{{Sfn|Rottman|2011|p=37}}

Modifications to the M16A2 were extensive. In addition to the then new STANAG 4172<ref>{{cite web| url = https://diweb.hq.nato.int/naag/Public%20Release%20Documents/AEP-97%20EDA%20V1%20E.pdf| title = STANAG 4172|archiveurl=https://web.archive.org/web/20230525142240/https://diweb.hq.nato.int/naag/Public%20Release%20Documents/AEP-97%20EDA%20V1%20E.pdf|archive-date=May 25, 2023}}</ref> 5.56×45mm NATO chambering and its accompanying rifling, the barrel was made with a greater thickness in front of the front sight post, to resist bending in the field and to allow a longer period of sustained fire without overheating. The rest of the barrel was maintained at the original thickness to enable the M203 grenade launcher to be attached. The barrel rifling was revised to a faster 1:7 (178&nbsp;mm) twist rate to adequately stabilize the new 5.56×45&nbsp;mm NATO SS109/M855 ball and L110/M856 tracer ammunition. The heavier longer SS109/M855 bullet reduced muzzle velocity from {{convert|3260|ft/s|m/s|0|abbr=on}}, to about {{convert|3110|ft/s|m/s|0|abbr=on}}.<ref name=Miller2002>{{cite book|author=David Miller|title=The Illustrated Directory of Special Forces|url=https://books.google.com/books?id=FMgpdulJsGgC&pg=PA280|access-date=6 June 2013|date=November 2002|publisher=Zenith Imprint|isbn=978-0-7603-1419-7|page=280|archive-url=https://web.archive.org/web/20130928225343/http://books.google.com/books?id=FMgpdulJsGgC&pg=PA280|archive-date=28 September 2013|url-status=live}}</ref>

A new adjustable rear sight was added, allowing the rear sight to be dialed in for specific range settings between 300 and 800 meters to take full advantage of the ballistic characteristics of the SS109/M855 rounds and to allow windage adjustments without the need of a tool or cartridge.<ref name=Venola>{{Cite journal |last1=Venola |first1=Richard |title=What a Long Strange Trip It's Been |journal=Book of the AR-15 |volume=1 |issue=2 |year=2005 |pages=6–18}}</ref> The flash suppressor was again modified, this time to be closed on the bottom, so the new birdcage-type muzzle device would not kick up dirt or snow when being fired from the prone position, and additionally act as an asymmetric recoil compensator to reduce muzzle climb.<ref>{{Harvnb|Hogg|Weeks|2000|p=292}}</ref><ref>{{Cite web|url=https://retrorifles.com/m16a2-flash-hiders/|title=M16A2 Flash Hiders|website=Retro Rifles|archiveurl=https://web.archive.org/web/20230321005819/https://retrorifles.com/m16a2-flash-hiders/|archive-date=March 21, 2023}}</ref>

A spent case deflector was incorporated into the upper receiver immediately behind the ejection port to prevent (hot) cartridge cases from striking left-handed users.<ref name="Venola, Richard 2005" /> The action was also modified, replacing the fully automatic setting with a three-round [[Engineering:Burst mode (weapons)|burst]] setting.<ref name=Venola /> When using a fully automatic weapon, inexperienced troops often hold down the trigger and "spray" when under fire. The U.S. Army concluded that three-shot groups provide an optimum combination of ammunition conservation, accuracy, and firepower.<ref>[https://robrobinette.com/M16_4-Way_Selector.htm M16 4-Way Selector Install (and everything you ever wanted to know about 3 and 4-way burst kits)] {{Webarchive|url=https://web.archive.org/web/20170630064206/https://robrobinette.com/M16_4-Way_Selector.htm |date=30 June 2017}}. Robrobinette.com. Retrieved: 20 November 2015.</ref>{{failed verification |date=July 2023}} The number of rounds fired in a burst is determined by a [[Engineering:Cam (mechanism)|cam]] mechanism that trips the trigger mechanism for each shot in the burst. For the burst the trigger must be held down for the full duration of the burst. The M16 series will terminate the burst if the trigger is released before the burst is complete but keep the cam in position. Thus, the next time the trigger is pulled, the weapon will only fire one or two rounds.<ref>{{cite web |url=http://www.ar15.com/content/guides/function/burst/ |title=:: Guides |publisher= |access-date=2012-01-06 |archive-url=https://web.archive.org/web/20120203232331/http://www.ar15.com/content/guides/function/burst/ |archive-date=2012-02-03 |url-status=dead }}</ref><ref>{{cite AV media |url=https://www.youtube.com/watch?v=cxwPEL8winI |archive-url=https://ghostarchive.org/varchive/youtube/20211218/cxwPEL8winI |archive-date=2021-12-18 |url-status=live|title=How 3-round burst works |date=23 September 2014 |publisher= |via=YouTube}}{{cbignore}}</ref> The USMC has retired the M16A2 in favor of the newer M16A4; a few M16A2s remain in service with the U.S. Army Reserve and National Guard,<ref>{{Cite web |url=https://media.voltron.voanews.com/Drupal/01live-166/styles/817x459/s3/2020-05/ap_nat_guard.jpg?itok=pmxzz2ym |title=Archived copy |access-date=31 May 2020 |archive-date=3 August 2020 |archive-url=https://web.archive.org/web/20200803191021/https://media.voltron.voanews.com/Drupal/01live-166/styles/817x459/s3/2020-05/ap_nat_guard.jpg?itok=pmxzz2ym |url-status=dead }}</ref><ref>{{Cite web |url=https://media.defense.gov/2018/Dec/04/2002069061/-1/-1/0/181101-A-VX503-452.JPG |title=National Guard rifleman |access-date=14 December 2018 |archive-url=https://web.archive.org/web/20181216031907/https://media.defense.gov/2018/Dec/04/2002069061/-1/-1/0/181101-A-VX503-452.JPG |archive-date=16 December 2018 |url-status=live|format=Photo}}</ref> {{wipe|United States Air Force}}, Navy and Coast Guard.{{Citation needed|date=April 2012}}

The handguard was modified from the original triangular shape to a round one, which better fit smaller hands and could be fitted to older models of the M16. The new handguards were also symmetrical, so armories need not separate left- and right-hand spares. The handguard retention ring was tapered to make it easier to install and uninstall the handguards.<ref name="Venola, Richard 2005" />

The new buttstock became ten times stronger than the original due to advances in polymer technology since the early 1960s. Original M16 stocks were made from cellulose-impregnated phenolic resin; the newer M16A2 stocks were engineered from DuPont [[Chemistry:Zytel|Zytel]] glass-filled thermoset polymers and became a replacement part for the preceding M16A1. The new buttstock was lengthened by {{convert|5/8|in|mm|sigfig=3|abbr=on}} and included a fully textured polymer buttplate for better grip on the shoulder and retained a panel for accessing a small compartment inside the stock, often used for storing a basic cleaning kit.<ref name="auto4">{{Cite web|url=https://books.google.com/books?id=_XajD07zIi8C&dq=m16a2+zytel&pg=PA144|title=Annual Department of Defense Bibliography of Logistics Studies and Related Documents|date=10 May 1991|publisher=United States Army Logistics Management Center.|via=Google Books|archive-date=June 20, 2023|archiveurl=https://web.archive.org/web/20230620180553/https://books.googleusercontent.com/books/content?req=AKW5Qadru3le86sHrR30bvU2BkHKeyNFKHKTVQknQvTVTidN4DDtjGrFYh8A_CA3dUDAlNhZbe1onJ7QItp6wxOFDQrmCsaaalzXCB8Y8swdrORL_kg1Qeo-HGrgEDgTfL5QfKYV0PfzyiOAWmLoRDP4j4_hdn3wUoXG9SC7mxkTs9lrNtHDkGWKLOIkoyBBtURMsPKAo4Vthps2jKWO744Lckk6OB94JPfwpRzaCVWk38fiMV76CO0Jlqb5rziJPPeSL0FtMMeTOORXYd3VM7osgVdGDHD-Kw}}</ref>

A notch for the middle finger was added to the pistol grip as well as more texture to enhance the grip. The new pistol grips were engineered from Zytel glass-filled thermoset polymers. The M16A2 pistol grip became a replacement part for the preceding M16A1.<ref name="Venola, Richard 2005" /><ref name="auto4"/>

The standard Model 645 M16A2 has a safe/semi/three-round burst selective fire trigger group. It became standard issue for the U.S. Marine Corps and Army.

There is also a safe/semi/three-round burst/automatic selective fire trigger group Model 708 version of M16A2 rifle named "M16A2 Enhanced", used by some militaries around the world.<ref name= hamanual>{{cite book|title=Hellenic Army Field Manual|publisher=Hellenic Army General Staff|date=December 2002|pages=[https://archive.org/details/ee-7-200/page/45/mode/2up 46–62]}}</ref>

===M16A3===
[[File:US Navy 071130-N-0555B-073 Aviation Boatswain's Mate (handling) Airman Jaime Chamorro fires an M-16.jpg|thumb|M16A3 with a Safe/Semi/Auto trigger group]]

The M16A3 is a modified version of the M16A2 adopted in small numbers by the U.S. Navy SEAL, Seabees, and security units.<ref name=did>{{Cite news |url=http://www.defenseindustrydaily.com/the-usas-m-16-rifle-purchases-04517/ |title=US Navy, Marines Buy M-16 Rifles |date=2 January 2008 |work=Defense Industry Daily |access-date=3 January 2008 |archive-url=https://web.archive.org/web/20080105151427/http://www.defenseindustrydaily.com/the-usas-m-16-rifle-purchases-04517/ |archive-date=5 January 2008 |url-status=live}}</ref> It features the M16A1 selective fire trigger group providing "safe", "semi-automatic" and "fully automatic" modes. Otherwise, it is externally similar to the M16A2.

===M16A4===
[[File:M16A4-JH01 noBG.jpg|thumb|right|M16A4 rifle with a removable carrying handle, polymer handguards and M7 bayonet mounted]]
[[File:The M16A4 Series 5.56mm Rifle.jpg|thumb|right|M16A4 rifle with ACOG sight, railed hand guard and foregrip]]

The M16A4 is the fourth generation of the M16 series. The iron sight/carrying handle assembly on the M16A2/M16A3 upper receiver, was replaced by a MIL-STD-1913 "Picatinny railed" flat-top upper receiver for mounting aiming optics or a removable iron sight/carrying handle assembly. The M16A4 rear aperture sights integrated in the Picatinny rail mounted carry handle assembly are adjustable from {{convert|300|m|yd|abbr=on}} up to {{convert|600|m|yd|abbr=on}}, where the further similar M16A2 iron sights line can reach up to {{convert|800|m|yd|abbr=on}}. The introduction of the Picatinny rail required the use of a higher F-marked front sight base to raise the post. The FN M16A4, using safe/semi/three-round burst selective fire, became standard issue for the U.S. Marine Corps.

Military issue rifles were also equipped with a full-length quad Knight's Armament Company M5 RAS Picatinny railed hand guard (that holds zero on the top rail), allowing vertical grips, lasers, tactical lights, and other accessories to be attached, coining the designation M16A4 MWS (or Modular Weapon System) in U.S. Army field manuals.{{citation needed|date=December 2022}}

Colt also produces M16A4 models for international purchases:
* R0901 / RO901/ NSN 1005-01-383-2872 (Safe/Semi/Auto)
* R0905 / RO905 (Safe/Semi/Burst)

A study of significant changes to Marine M16A4 rifles released in February 2015 outlined several new features that could be added from inexpensive and available components. Those features included: a muzzle compensator in place of the flash suppressor to manage recoil and allow for faster follow-on shots, though at the cost of noise and flash signature and potential overpressure in close quarters; a heavier and/or [[Engineering:Free-floating barrel|free-floating barrel]] to increase accuracy from 4.5 MOA (Minute(s) Of Angle) to potentially 2 MOA; changing the reticle on the Rifle Combat Optic from chevron-shaped to a semi-circular reticle with a dot at the center used in the M27 IAR's Squad Day Optic so as not to obscure the target at long distance; using a trigger group with a more consistent pull force, even a reconsideration of the burst capability; and the addition of ambidextrous charging handles and bolt catch releases for easier use with left-handed shooters.<ref>{{cite news|url=http://www.marinecorpstimes.com/story/military/tech/2015/02/16/deadlier-rifles-ammo-may-way/23369675/ |title=Deadlier rifles and ammo may be on the way|archive-url=https://web.archive.org/web/20170708125903/https://www.marinecorpstimes.com/story/military/tech/2015/02/16/deadlier-rifles-ammo-may-way/23369675/ |archive-date=8 July 2017 |work=Marine Corps Times|date=16 February 2015|url-status=live}}</ref>

In 2014, Marine units were provided with a limited number of adjustable stocks in place of the traditional fixed stock for their M16A4s to issue to smaller Marines who would have trouble comfortably reaching the trigger when wearing body armor. The adjustable stocks were added as a standard authorized accessory, meaning units can use operations and maintenance funds to purchase more if needed.<ref>{{cite news |url=http://www.marinecorpstimes.com/story/military/tech/2015/09/17/marines-unveil-plan-modernize-their-small-arms-arsenal/72006282/ |title=Marines unveil plan to modernize their small arms arsenal |archive-url=https://web.archive.org/web/20160105102710/http://www.marinecorpstimes.com/story/military/tech/2015/09/17/marines-unveil-plan-modernize-their-small-arms-arsenal/72006282/ |archive-date=5 January 2016 |work=Marine Corps Times|date=17 September 2015|url-status=live}}</ref>

The Marine Corps had long maintained the full-length M16 as their standard infantry rifle, but in October 2015 the switch to the M4 carbine was approved as the standard-issue weapon, giving Marine infantry a smaller and more compact weapon. Enough M4s were already in the inventory to re-equip all necessary units by September 2016, and M16A4s were moved to support<ref name="militarytimes26oct15">{{cite news |url=https://www.marinecorpstimes.com/story/military/2015/10/26/commandant-approves-m4-standard-rifle-marine-corps-infantry/74593750/ |title=Commandant approves M4 as standard weapon for Marine infantry|archive-url=https://web.archive.org/web/20170509081237/http://www.marinecorpstimes.com/story/military/2015/10/26/commandant-approves-m4-standard-rifle-marine-corps-infantry/74593750/ |archive-date=9 May 2017 |work=Military Times|date=26 October 2015|url-status=live}}</ref><ref>{{cite news |url=http://www.militarytimes.com/story/military/2015/07/27/marine-officials-endorse-infantry-plan--ditch-m16--m4/30145257/|title=Marine brass endorses infantry plan to ditch M16 for M4 |archive-url=https://web.archive.org/web/20150730224707/http://www.militarytimes.com/story/military/2015/07/27/marine-officials-endorse-infantry-plan--ditch-m16--m4/30145257/ |archive-date=30 July 2015|work=Military Times |date=27 July 2015|url-status=dead}}</ref> and non-infantry Marines.<ref>{{cite news |url=http://www.marinecorpstimes.com/story/military/tech/2015/11/01/marine-grunts-react-switch-m16-m4/74849998/ |title=Marine grunts react to switch from the M16 to the M4 |archive-url=https://web.archive.org/web/20160425045929/http://www.marinecorpstimes.com/story/military/tech/2015/11/01/marine-grunts-react-switch-m16-m4/74849998/ |archive-date=25 April 2016 |work=Marine Corps Times |date=1 November 2015 |url-status=dead |access-date=2 November 2015}}</ref>

===Summary of differences===
{| class="wikitable"
|-
! Colt model no.
! Military designation
! 20" Barrel w/ bayonet lug
! Handguard type
! Buttstock type
! Pistol grip type
! Lower receiver type
! Upper receiver type
! Rear sight type
! Front sight type
! Muzzle device
! Forward assist?
! Case deflector?
! Trigger pack
|-
|601
|AR-15 Designated M16 on 3 Dec 1963
|A1 profile (1:14 twist)
|Green or brown full-length triangular
|Green or brown fixed A1
|A1
|A1
|A1
|A1
|A1
|Duckbill flash suppressor
|No
|No
|Safe/Semi/Auto
|-
|602
|AR-15 Designated M16 3 Dec 1963 - there was no XM16
|A1 profile (1:12 twist)
|Full-length triangular
|Fixed A1
|A1
|A1
|A1
|A1
|A1
|Duckbill or three-prong flash suppressor
|No
|No
|Safe/Semi/Auto
|-
|603
|XM16E1 designation changed to M16A1 Feb1967 with standardisation
|A1 profile (1:12 twist)
|Full-length triangular
|Fixed A1
|A1
|A1
|A1
|A1
|A1
|Three-prong or M16A1 birdcage flash suppressor
|Yes
|No
|Safe/Semi/Auto
|-
|603
|M16A1
|A1 profile (1:12 twist)
|Full-length triangular
|Fixed A1
|A1
|A1
|A1
|A1
|A1
|Three-prong or birdcage flash suppressor
|Yes
|Yes or No
|Safe/Semi/Auto
|-
|604
|M16
|A1 profile (1:12 twist)
|Full-length triangular
|Fixed A1
|A1
|A1
|A1
|A1
|A1
|Three-prong or M16A1-style birdcage flash suppressor
|No
|No
|Safe/Semi/Auto
|-
|645
|M16A1E1/PIP
|A2 profile (1:7 twist)
|Full-length ribbed
|Fixed A2
|A1
|A1 or A2
|A1 or A2
|A1 or A2
|A2
|M16A1 or M16A2-style birdcage flash suppressor
|Yes
|Yes or No
|Safe/Semi/Auto or Safe/Semi/Burst
|-
|645
|M16A2
|A2 profile (1:7 twist)
|Full-length ribbed
|Fixed A2
|A2
|A2
|A2
|A2
|A2
|M16A2-style birdcage flash suppressor
|Yes
|Yes
|Safe/Semi/Burst or Safe/Semi/Burst/Auto
|-
|708
|M16A2 ENHANCED
|A2 profile (1:7 twist)
|Full-length ribbed
|Fixed A2
|A2
|A2
|A2
|A2
|A2
|M16A2-style birdcage flash suppressor
|Yes
|Yes
|Safe/Semi/Burst/Auto
|-
|645E
|M16A2E1
|A2 profile (1:7 twist)
|Full-length ribbed
|Fixed A2
|A2
|A2
|Flattop with Colt Rail
|Flip-up
|Folding
|M16A2-style birdcage flash suppressor
|Yes
|Yes
|Safe/Semi/Burst or Safe/Semi/Burst/Auto
|-
|N/A
|M16A2E2
|A2 profile (1:7 twist)
|Full-length semi-beavertail w/ HEL guide
|Retractable ACR
|ACR
|A2
|Flattop with Colt rail
|None
|A2
|ACR muzzle brake
|Yes
|Yes
|Safe/Semi/Burst or Safe/Semi/Burst/Auto
|-
|646
|M16A3 (M16A2E3)
|A2 profile (1:7 twist)
|Full-length ribbed
|Fixed A2
|A2
|A2
|A2
|A2
|A2
|M16A2-style birdcage flash suppressor
|Yes
|Yes
|Safe/Semi/Auto
|-
|655
|M16A1 Special High Profile
|HBAR profile <br />(1:12 twist)
|Full-length triangular
|Fixed A1
|A1
|A1
|A1
|A1
|A1
|M16A1-style birdcage flash suppressor
|Yes
|No
|Safe/Semi/Auto
|-
|656
|M16A1 Special Low Profile
|HBAR profile <br />(1:12 twist)
|Full-length triangular
|Fixed A1
|A1
|A1
|A1 with modified Weaver base
|Low Profile A1
|Hooded A1
|M16A1-style birdcage flash suppressor
|Yes
|No
|Safe/Semi/Auto
|-
|945
|M16A4 (M16A2E4)
|A2 profile (1:7 twist)
|Full-length ribbed or KAC M5 RAS
|Fixed A2/M4 Collapsed stock
|A2
|A2
|Flattop with MIL-STD-1913 rail
|None
|A4
|M16A2-style birdcage flash suppressor
|Yes
|Yes
|Safe/Semi/Auto (RO901) or Safe/Semi/Burst (RO905)
|}

==Derivatives==
===Colt Commando (XM177 & GAU-5)===
[[File:CCTwithGAU-5.jpg|thumb|A USAF Combat Control Team member with a GAU-5 carbine and oversized flash suppressor]]

In Vietnam, some soldiers were issued a [[Engineering:Carbine|carbine]] version of the M16 named XM177. The XM177 had a shorter {{convert|10|in|mm|0|abbr=on}} barrel and a telescoping stock, which made it substantially more compact. It also possessed a combination flash hider/sound moderator to reduce problems with muzzle flash and loud report. The Air Force's GAU-5/A (XM177) and the Army's XM177E1 variants differed over the latter's inclusion of a forward assist, although some GAU-5s do have the forward assist. The final Air Force GAU-5/A and Army XM177E2 had an {{convert|11.5|in|mm|0|abbr=on}} barrel with a longer flash/sound suppressor. The lengthening of the barrel was to support the attachment of Colt's own [[Engineering:XM148 grenade launcher|XM148]] 40&nbsp;mm grenade launcher. These versions were also known as the Colt Commando model commonly referenced and marketed as the CAR-15. The variants were issued in limited numbers to special forces, helicopter crews, Air Force pilots, Air Force Security Police Military Working Dog (MWD) handlers, officers, radio operators, artillerymen, and troops other than front line riflemen. Some USAF GAU-5A/As were later equipped with even longer {{convert|14.5|in|mm|adj=on}} 1/12 rifled barrels as the two shorter versions were worn out. The {{convert|14.5|in|mm|adj=on}} barrel allowed the use of MILES gear and for bayonets to be used with the sub-machine guns (as the Air Force described them). By 1989, the Air Force started to replace the earlier barrels with 1/7 rifled models for use with the M855-round. The weapons were given the redesignation of GUU-5/P.

These were used by the British Special Air Service during the Falklands War.<ref name=special_operations1 />

===M4 carbine===
{{Main|Engineering:M4 carbine}}
[[File:SCRange20034344940.jpg|thumb|right|An M4A1 carbine (foreground) and two M16A2s (background) being fired by U.S. Marines during a live fire exercise: though adopted in the 1990s and derived from the M16A2, the M4 carbine was part of a long line of short-barreled AR-15 used in the U.S. military]]

The M4 carbine was developed from various outgrowths of these designs, including a number of {{convert|14.5|in|mm|0|adj=on}}-barreled A1 style carbines. The XM4 (Colt Model 720) started its trials in 1984, with a barrel of {{convert|14.5|in|mm}}. The weapon became the M4 in 1991. Officially adopted as a replacement for the M3 "Grease Gun" (and the Beretta M9 and M16A2 for select troops) in 1994, it was used with great success in the Balkans and in more recent conflicts, including the Afghanistan and Iraq theaters. The M4 carbine has a three-round burst firing mode, while the M4A1 carbine has a [[Engineering:Automatic firearm|fully automatic]] firing mode. Both have a Picatinny rail on the upper receiver, allowing the carry handle/rear sight assembly to be replaced with other sighting devices.

====M4 Commando====
Colt also returned to the original "Commando" idea, with its Model 733, essentially a modernized XM177E2 with many of the features introduced on the M16A2.

===M5 carbine===
[[File:Colt M5 at IDEX 2023.jpg|thumb|right|M5 carbine]]
The M5 carbine system was developed by Colt as an improvement on the M4 carbine. It incorporates a fully ambidextrous lower receiver, free-floating barrel and lengthened upper rail. The M5 carbine has four possible barrel lengths: 10.3, 11.5, 14.5 and 16.1 inches. Other M5 variants and calibers are the: M5 SCW (Sub-compact weapon) (5.56x45mm); M5 300 (.300 AAC Blackout); M5 SMG (9x19mm); CMK (7.62x39mm); M7 Battle Rifle (7.62x51mm) and Designated Marksman and Semi-Automatic Sniper System (both 5.56x45mm).

===Diemaco C7 and C8===
{{Main|Engineering:Colt Canada C7 and C8}}
[[File:Canadian C7A2 Rifle.JPG|thumb|A Canadian soldier fires the current issue C7A2 rifle at the range with a [[Engineering:C79 optical sight|C79]]A2 sight. This particular example is missing the standard TRIAD mount.]]

The Diemaco C7 and C8 are updated variants of the M16 developed and used by the Canadian Forces and are now manufactured by Colt Canada. The C7 is a further development of the experimental M16A1E1. Like earlier M16s, it can be fired in either semi-automatic or automatic mode, instead of the burst function selected for the M16A2. The C7 also features the structural strengthening, improved handguards, and longer stock developed for the M16A2. Diemaco changed the trapdoor in the buttstock to make it easier to access and a spacer of {{convert|0.5|in|mm}} is available to adjust stock length to user preference. The most easily noticeable external difference between American M16A2s and Diemaco C7s is the retention of the A1 style rear sights. Not easily apparent is Diemaco's use of hammer-forged barrels. The Canadians originally desired to use a heavy barrel profile instead.

The C7 has been developed to the C7A1, with a Weaver rail on the upper receiver for a C79 3.4×28 optical sight, and to the C7A2, with different furniture and internal improvements. The Diemaco produced Weaver rail on the original C7A1 variants does not meet the M1913 "Picatinny" standard, leading to some problems with mounting commercial sights. This is easily remedied with minor modification to the upper receiver or the sight itself. Since Diemaco's acquisition by Colt to form Colt Canada, all Canadian produced flattop upper receivers are machined to the M1913 standard.

The C8 is the carbine version of the C7.<ref>[http://www.casr.ca/101-army-smallarm-1.htm Canadian Forces Automatic Rifles] {{webarchive|url=https://web.archive.org/web/20110706171606/http://casr.ca/101-army-smallarm-1.htm |date=6 July 2011}}. Canadian American Strategic Review. Retrieved: 23 August 2009.</ref> The C7 and C8 are also used by ''Hærens Jegerkommando'', ''Marinejegerkommandoen'' and FSK (Norway), Denmark's Armed Forces (all branches), and the Netherlands Armed Forces as its main infantry weapon. Following trials, variants became the weapon of choice of the British SAS.

===Mk 4 Mod 0===
The Mk 4 Mod 0 was a variant of the M16A1 produced for the U.S. Navy SEALs during the Vietnam War and adopted in April 1970. It differed from the basic M16A1 primarily in being optimized for maritime operations and coming equipped with a sound suppressor. Most of the operating parts of the rifle were coated in Kal-Guard, a hole of {{convert|0.25|in|mm}} was drilled through the stock and buffer tube for drainage, and an O-ring was added to the end of the buffer assembly. The weapon could reportedly be carried to the depth of {{convert|200|ft|m}} in water without damage. The initial Mk 2 Mod 0 Blast Suppressor was based on the U.S. Army's Human Engineering Lab's (HEL) M4 noise suppressor. The HEL M4 vented gas directly from the action, requiring a modified bolt carrier. A gas deflector was added to the charging handle to prevent gas from contacting the user. Thus, the HEL M4 suppressor was permanently mounted though it allowed normal semi-automatic and automatic operation. If the HEL M4 suppressor were removed, the weapon would have to be manually loaded after each single shot. On the other hand, the Mk 2 Mod 0 blast suppressor was considered an integral part of the Mk 4 Mod 0 rifle, but it would function normally if the suppressor were removed. The Mk 2 Mod 0 blast suppressor also drained water much more quickly and did not require any modification to the bolt carrier or to the charging handle. In the late 1970s, the Mk 2 Mod 0 blast suppressor was replaced by the Mk 2 blast suppressor made by Knight's Armament Company (KAC). The KAC suppressor can be fully submerged and water will drain out in less than eight seconds. It will operate without degradation even if the rifle is fired at the maximum rate of fire. The U.S. Army replaced the HEL M4 with the much simpler Studies in Operational Negation of Insurgency and Counter-Subversion (SIONICS) MAW-A1 noise and flash suppressor.

===US Navy Mk 12 Special Purpose Rifle===
[[File:SPRCrane.jpg|thumb|US Navy Mk 12 Special Purpose Rifle]]

Developed to increase the effective range of soldiers in the designated marksman role, the U.S. Navy developed the Mark 12 Special Purpose Rifle (SPR). Configurations in service vary, but the core of the Mark 12 SPR is an 18" heavy barrel with muzzle brake and free float tube. This tube relieves pressure on the barrel caused by standard handguards and greatly increases the potential accuracy of the system. Also common are higher magnification optics ranging from the 6× power Trijicon ACOG to the Leupold Mark 4 Tactical rifle scopes. Firing Mark 262 Mod 0 ammunition with a 77gr Open tip Match bullet, the system has an official effective range of 600+ meters. However, published reports of confirmed kills beyond 800&nbsp;m from Iraq and Afghanistan were not uncommon.{{Citation needed|date=May 2010}}

===M231 Firing Port Weapon (FPW)===
[[File:M231 1.svg|thumb|right|M231 FPW]]

The [[Engineering:M231 Firing Port Weapon|M231 Firing Port Weapon]] (FPW) is an adapted version of the M16 assault rifle for firing from ports on the [[Engineering:M2 Bradley|M2 Bradley]]. The infantry's normal M16s are too long for use in a "buttoned up" fighting vehicle, so the FPW was developed to provide a suitable weapon for this role.

===Colt Model 655 and 656 "Sniper" variants===
With the expanding Vietnam War, Colt developed two rifles of the M16 pattern for evaluation as possible light sniper or designated marksman rifles. The Colt Model 655 M16A1 Special High Profile was essentially a standard A1 rifle with a heavier barrel and a scope bracket that attached to the rifle's carry handle. The Colt Model 656 M16A1 Special Low Profile had a special upper receiver with no carrying handle. Instead, it had a low-profile iron sight adjustable for windage and a Weaver base for mounting a scope, a precursor to the Colt and Picatinny rails. It also had a hooded front iron sight in addition to the heavy barrel. Both rifles came standard with either a Leatherwood/Realist scope 3–9× Adjustable Ranging Telescope. Some of them were fitted with a Sionics noise and flash suppressor. Neither of these rifles were ever standardized.

These weapons can be seen in many ways to be predecessors of the U.S. Army's SDM-R and the USMC's SAM-R weapons.

===Others===
* The Chinese Norinco CQ is an unlicensed derivative of the M16A1 made specifically for export, with the most obvious external differences being in its handguard and [[Engineering:Revolver|revolver]]-style pistol grip.
** The '''ARMADA rifle''' (a copy of the Norinco CQ) and '''TRAILBLAZER carbine''' (a copy of the Norinco CQ Type A) are manufactured by S.A.M. – Shooter's Arms Manufacturing, a.k.a. Shooter's Arms Guns & Ammo Corporation, headquartered in Metro Cebu, Republic of the Philippines.
** The '''S-5.56 rifle''', a clone of the Type CQ, is manufactured by the Defense Industries Organization of [[Religion:Iran|Iran]]. The rifle itself is offered in two variants: the '''S-5.56 A1''' with a 19.9-inch barrel and 1:12 pitch rifling (1 turn in 305&nbsp;mm), optimized for the use of the M193 Ball cartridge; and the '''S-5.56 A3''' with a 20-inch barrel and a 1:7 pitch rifling (1 turn in 177, 8&nbsp;mm), optimized for the use of the SS109 cartridge.<ref>{{cite web|url=http://www.irandefence.net/attachment.php?attachmentid=3576&stc=1&d=116645856|title=S-5.56 rifle technical specifics table|archive-url=https://web.archive.org/web/20170630215544/http://www.irandefence.net/attachment.php?attachmentid=3576&stc=1&d=116645856' |archive-date=30 June 2017 |access-date=7 October 2007}}</ref>
** The '''KH-2002''' is an Iranian [[Engineering:Bullpup|bullpup]] conversion of the locally produced S-5.56 rifle. Iran intends to replace the standard issue weapon of its armed forces with this rifle.
** The '''Terab rifle''' is a copy of the '''DIO S-5.56''' manufactured by the Military Industry Corporation of Sudan.<ref>{{cite web |title=Product Details: Terab|url=http://www.mic.sd/pages/en/product/productDetails/5|access-date=16 November 2016|url-status=dead|archive-url=https://web.archive.org/web/20170110012904/http://www.mic.sd/pages/en/product/productDetails/5|archive-date=10 January 2017}}</ref>
* The '''M16S1''' is the M16A1 rifle made under license by [[Company:ST Kinetics|ST Kinetics]] in Singapore. It was the standard issue weapon of the Singapore Armed Forces. It is being replaced by the newer SAR 21 in most branches. It is, in the meantime, the standard issue weapon in the reserve forces.
* The MSSR rifle is a sniper rifle developed by the Philippine Marine Corps Scout Snipers that serves as their primary sniper weapon system. 
* The Special Operations Assault Rifle (SOAR) assault carbine was developed by Ferfrans based on the M16 rifle. It is used by the Special Action Force of the Philippine National Police.
* Taiwan uses piston-driven M16-based weapons as their standard rifle. These include the T65, T86 and T91 assault rifles.
* Ukraine has announced plans in January 2017 for Ukroboronservis and Aeroscraft to produce the [[Engineering:M4-WAC-47|M16 WAC47]], an accurized M4 variation that uses standard 7.62×39&nbsp;mm AK-47 magazines.<ref>{{cite press release|url=http://ukroboronprom.com.ua/en/media/m16-wac-47-dlya-ukrayinskoyi-armiyi-vid-dk-ukroboronprom.html|title=M16 – WAC-47 for Ukrainian army from UkrOboronProm|publisher=UkrOboronProm|date=10 January 2017|access-date=10 January 2017|archive-url=https://web.archive.org/web/20170118163054/http://ukroboronprom.com.ua/en/media/m16-wac-47-dlya-ukrayinskoyi-armiyi-vid-dk-ukroboronprom.html|archive-date=18 January 2017|url-status=dead}}</ref><ref>{{cite web|url=http://dailysignal.com/2017/01/10/ukraines-plan-to-manufacture-us-m16-combat-rifles-hits-a-snag-over-ammunition/|title=Ukraine's Plan to Manufacture US M16 Rifles Hits a Snag|website=dailysignal.com|date=11 January 2017|access-date=23 January 2017|archive-url=https://web.archive.org/web/20170114234053/http://dailysignal.com/2017/01/10/ukraines-plan-to-manufacture-us-m16-combat-rifles-hits-a-snag-over-ammunition/|archive-date=14 January 2017|url-status=dead}}</ref>
* New Zealand has adopted the Lewis Machine and Tool Company's upgraded version of the M16 system to replace the [[Engineering:Steyr AUG|Steyr AUG]]. This CQB16 rifle will be fielded in 2017 and is named MARS-L (Modular Ambidextrous Rifle System-Light).

==Production and users==
[[File:M16 operators of the world.svg|thumb|upright=1.8|Worldwide users of the M16 (former and current)]]

The M16 is the most commonly manufactured 5.56×45&nbsp;mm rifle in the world. Currently, the M16 is in use by 15 NATO countries and more than 80 countries worldwide. Together, numerous companies in the United States, Canada, and China have produced more than 8,000,000 rifles of all variants. Approximately 90% are still in operation.<ref name=colt_customers>{{cite web |url=http://www.colt.com/mil/customers.asp |title=Customers / Weapon users |website=Colt Defense Weapon Systems |archive-url=https://web.archive.org/web/20110902033712/http://www.colt.com/mil/customers.asp |archive-date=2 September 2011}}</ref> The M16 replaced both the M14 rifle and M2 carbine as standard infantry rifle of the U.S. armed forces. Although, the M14 continues to see limited service, mostly in sniper, designated marksman, and ceremonial roles.

===Users===
[[File:140311-M-YZ032-904 (13218013143).jpg|thumb|Afghan National Army soldiers with M16A2 rifles]]
[[File:LAV3patrol.jpg|thumb|Canadian soldiers patrol Kandahar Afghanistan armed with C7 (M16 type) rifles]]
[[File:CARAT Malaysia 2008 (080715-N-4431B-568).jpg|thumb|right|Malaysian Army soldier with an M16A1 equipped with an M203 grenade launcher during a CARAT Malaysia 2008]]
[[File:Flickr - Israel Defense Forces - Female Soldiers Practice Shooting (1).jpg|thumb|Soldiers of the Israel Defense Forces in training with M16A1 rifles with the A2 style handguard]]
[[File:RP Marines assault line DM-SD-06-10463.JPEG|thumb|Philippine marines using M16A1 rifles with the A2 style handguard during a military exercise]]
[[File:2013.10.1 건군 제65주년 국군의 날 행사 The celebration ceremony for the 65th Anniversary of ROK Armed Forces (10078325636).jpg|thumb|South Korean soldiers toss bayonet mounted M16 rifles into the air at the celebration ceremony for the 65th Anniversary of the South Korean armed forces]]
[[File:ARVN Rangers defend Saigon, Tet Offensive.jpg|thumb|Vietnamese Army (ARVN) Rangers armed with M16s defend Saigon during the Tet Offensive]]
[[File:US Marine M16A4 Rifle ACOG.jpg|thumb|right|United States Marine firing an M16A4 equipped with an ACOG]]
[[File:Paskibra Pasukan 45.jpg|thumb|Indonesian soldiers accompanying the Heritage Flag Hoisting Troops are seen holding M16A1 and SS1 rifles while marching]]
<!-- READ FIRST: This section is for cited entries only. Please do not add entries into this list without a citation from a reliable source. All entries without a citation will be removed. Thank you. 
-->
* {{flag|Afghanistan}}: Taliban use M16A2 and M16A4 rifles previously supplied for Afghan National Army. Also in use with the Badri 313 Battalion.<ref>{{cite web|url=https://www.wionews.com/south-asia/explainer-what-is-badri-313-unit-talibans-so-called-special-force-409665|title=Explainer: What is Badri 313 unit? Taliban's so-called 'special force'|publisher=WION|archive-url=https://web.archive.org/web/20221023174713/https://www.wionews.com/south-asia/explainer-what-is-badri-313-unit-talibans-so-called-special-force-409665|archive-date= 23 October 2022}}</ref>
*{{Flag|Albania}}<ref name=":0">{{Cite web|last=|first=|date=|title=AR 15 (M16/M4)|url=https://salw-guide.bicc.de/en/weapon/view/27/ar-15-m16-m4|access-date=|website=SALW Guide}}</ref>
*{{Flag|Antigua and Barbuda}}<ref name=":0" />
* {{flag|Argentina}}: Currently use the M16A2 (by all Armed Forces).<ref>{{cite web |url=http://saorbats.com.ar/GaleriaSaorbats/EA05/EA05/index.html |title=Exposición del Ejército Argentino en Palermo, Buenos Aires- Mayo de 2005 |access-date=27 September 2011 |url-status=dead |archive-url=https://web.archive.org/web/20090122004105/http://saorbats.com.ar/GaleriaSaorbats/EA05/EA05/index.html |archive-date=22 January 2009 }}. saorbats.com.ar</ref>
* {{flag|Azerbaijan}}: M16A4, used by the special forces and State Border Service (DSX).<ref>{{Cite web|url=https://aqreqator.az/az/siyaset/862891|title = DSX silahlanmasında ABŞ istehsalı tüfəng - M16 (ARAŞDIRMA)}}</ref>
* {{flag|Bahrain}}<ref>{{cite journal|last=|first=|date=23 November 2011|title=Report of the Bahrain Independent Commission of Inquiry|url=http://files.bici.org.bh/BICIreportEN.pdf|url-status=dead|journal=|publisher=Bahrain Independent Commission of Inquiry|volume=|pages=77, 236, 262|archive-url=https://web.archive.org/web/20111219203044/http://files.bici.org.bh/BICIreportEN.pdf|archive-date=19 December 2011|access-date=26 December 2011|via=}}</ref>
* {{flag|Bangladesh}}<ref name=":0" />
*{{flag|Barbados}}<ref name="ewen2005">Jane's Special Forces Recognition Guide, Ewen Southby-Tailyour (2005) p. 446.</ref>
* {{flag|Bosnia and Herzegovina}}:<ref name=ewen2005 /> M16A1/A4<ref>{{cite web|url=http://zeljeznopolje.com/vijesti/bih/item/321-ministarstvo-odbrane-izmjenom-propisa-vojnici-ce-moci-ostati-u-osbih-i-nakon-35-godine|title=Ministarstvo odbrane: Izmjenom propisa vojnici će moći ostati u OSBiH i nakon 35. godine|last=DH|website=zeljeznopolje.com|access-date=28 April 2019|archive-url=https://web.archive.org/web/20190428024651/http://zeljeznopolje.com/vijesti/bih/item/321-ministarstvo-odbrane-izmjenom-propisa-vojnici-ce-moci-ostati-u-osbih-i-nakon-35-godine|archive-date=28 April 2019|url-status=dead}}</ref>
* {{flag|Belize}}<ref name=ewen2005 />
* {{flag|Bolivia}}<ref name=ewen2005 /> M16A1/A2
* {{flag|Brazil}}: Used by special forces in the final phase of the Araguaia guerrilla war.<ref name=":1" /> M16A2s used by Brazilian Marine Corps<ref name ='SAS 2007 9'>{{cite book|url=http://www.smallarmssurvey.org/publications/by-type/yearbook/small-arms-survey-2007.html|chapter-url=http://www.smallarmssurvey.org/fileadmin/docs/A-Yearbook/2007/en/full/Small-Arms-Survey-2007-Chapter-09-EN.pdf|chapter=Enemy Within: Ammunition Diversion in Uganda and Brazil|title=The Small Arms Survey 2007: Guns and the City|publisher={{wipe|Cambridge University Press}}|year=2007|author=Small Arms Survey|page=309|isbn=978-0-521-88039-8|access-date=29 August 2018|archive-url=https://web.archive.org/web/20180827001033/http://www.smallarmssurvey.org/publications/by-type/yearbook/small-arms-survey-2007.html|archive-date=27 August 2018|url-status=dead|}}</ref>
* {{flag|Brunei}}<ref name=ewen2005 /> M16A2 is used by the Royal Brunei Armed Forces as their main service rifle.<ref>{{Cite web|url=https://openresearch-repository.anu.edu.au/bitstream/1885/216596/1/146_Small_arms_production_and_transfers_in_Southeast_Asia.pdf&ved=2ahUKEwiq99zLzObxAhWBXisKHY-HC0gQFnoECCIQAQ&usg=AOvVaw2pI2828wbF5cH6G1l8c4Ew|title=Small arms production and transfers in Southeast Asia - ANU Open Research}} </ref>
* {{flag|Burundi}}: Burundian rebels<ref name ='SAS 2007 6'>{{cite book|url=http://www.smallarmssurvey.org/publications/by-type/yearbook/small-arms-survey-2007.html|chapter-url=http://www.smallarmssurvey.org/fileadmin/docs/A-Yearbook/2007/en/full/Small-Arms-Survey-2007-Chapter-06-EN.pdf|chapter=Armed Violence in Burundi: Conflict and Post-Conflict Bujumbura|title=The Small Arms Survey 2007: Guns and the City|publisher={{wipe|Cambridge University Press}}|year=2007|author=Small Arms Survey|page=204|isbn=978-0-521-88039-8|access-date=29 August 2018|archive-url=https://web.archive.org/web/20180827001033/http://www.smallarmssurvey.org/publications/by-type/yearbook/small-arms-survey-2007.html|archive-date=27 August 2018|url-status=live|}}</ref>
* {{flag|Cambodia}}<ref name=worldpolicy2000>{{cite web |url=http://www.worldpolicy.org/projects/arms/reports/smallarms.htm |title=Report: Profiling the Small Arms Industry – World Policy Institute – Research Project |date=November 2000 |publisher=World Policy Institute |access-date=15 July 2010 |archive-url=https://web.archive.org/web/20171011093831/http://www.worldpolicy.org/projects/arms/reports/smallarms.htm |archive-date=11 October 2017 |url-status=dead}}</ref><ref>{{cite web |url=http://www.smallarmssurvey.org/files/sas/publications/w_papers_pdf/WP/WP4_Cambodia.pdf |title=How Many Weapons Are There in Cambodia? |author1=Wille, Christina|format=Working Paper |archive-url=https://web.archive.org/web/20100704230440/http://www.smallarmssurvey.org/files/sas/publications/w_papers_pdf/WP/WP4_Cambodia.pdf |archive-date=4 July 2010 |website=Small Arms Survey |date=5 May 2011|url-status=dead |access-date=27 September 2011}}</ref> M16A1
* {{flag|Cameroon}}<ref name=ewen2005 />
* {{flag|Canada}}: [[Engineering:Colt Canada C7 and C8|Colt Canada C7 and C8]] variants made by Colt Canada are used by the Canadian Forces.<ref name=miller2001>Miller, David (2001). ''The Illustrated Directory of 20th Century Guns''. Salamander Books Ltd. {{ISBN|1-84065-245-4}}.</ref>
* {{CAF}}<ref name ='SAS 2005'>{{cite book|url=http://www.smallarmssurvey.org/publications/by-type/yearbook/small-arms-survey-2005.html|chapter-url=http://www.smallarmssurvey.org/fileadmin/docs/A-Yearbook/2005/en/Small-Arms-Survey-2005-Chapter-11-EN.pdf|chapter=The Central African Republic: A Case Study of Small Arms and Conflict|title=Small Arms Survey 2005: Weapons at War|publisher=[[Organization:Oxford University Press|Oxford University Press]]|year=2005|author=Small Arms Survey|page=318|isbn=978-0-19-928085-8|access-date=29 August 2018|archive-url=https://web.archive.org/web/20180830004838/http://www.smallarmssurvey.org/publications/by-type/yearbook/small-arms-survey-2005.html|archive-date=30 August 2018|url-status=dead|}}</ref>
* {{flag|Chile}}<ref name=ewen2005 /> M16A1 used by Chilean Marine Corps.
* {{Flag|Colombia}}<ref name=":0" />
* {{flag|Congo-Kinshasa}}<ref name=worldpolicy2000 />
* {{flag|Costa Rica}}<ref name=colt_customers />
* {{Flag|Czech Republic}}<ref name=":0" />
* {{flag|Denmark}}:<ref name="ewen2005" />
* {{Flag|Djibouti}}<ref name=":0" />
* {{flag|Dominican Republic}}<ref name=ewen2005 />
* {{flag|East Timor}}<ref>''Jane's Sentinel Security Assessment – Southeast Asia''. Issue 20 – 2007. pp. 146, 152.</ref> M16A2
* {{flag|Ecuador}}<ref name=ewen2005 />
* {{Flag|Egypt}}<ref name=":0" />
* {{flag|El Salvador}}<ref name=ewen2005 /> M16A1/A2/A3/A4<ref>{{cite magazine|title=El Salvador: Standing Talls|magazine=Small Arms Defense Journal|date=12 January 2012|first=Julio A.|last=Montes|url=http://www.sadefensejournal.com/wp/?p=952|volume=3|issue=4|access-date=19 January 2019|archive-url=https://web.archive.org/web/20190417231939/http://www.sadefensejournal.com/wp/?p=952|archive-date=17 April 2019|url-status=live}}</ref>
* {{flag|Estonia}}<ref>{{cite web |url=http://www.mil.ee/?menu=tehnika1&sisu=m16a1 |title=Eesti Kaitsevägi – Tehnika – Automaat M-16 A1 |publisher=Mil.ee |access-date=8 September 2008 |archive-url=https://web.archive.org/web/20080603130721/http://www.mil.ee/?menu=tehnika1&sisu=m16a1 |archive-date=3 June 2008 |url-status=dead}}</ref> Ex-U.S. M16A1s
*{{Flag|Falkland Islands}}<ref name=":0" />
* {{flag|Fiji}}<ref name=ewen2005 /> M16A1/A2
* {{flag|France}}: Used by counter-terrorism and special operations forces<ref>{{cite web|title=M16 723 M203|date=13 July 2016|url=https://www.defense.gouv.fr/terre/equipements/materiels-specifiques/forces-speciales/armement/m16-723-m203|website=defense.gouv.fr|publisher=Ministère des Armées|access-date=30 January 2019|archive-url=https://web.archive.org/web/20190130222048/https://www.defense.gouv.fr/terre/equipements/materiels-specifiques/forces-speciales/armement/m16-723-m203|archive-date=30 January 2019|url-status=live}}</ref><ref name=ewen2005 />
* {{flag|Gabon}}<ref name=ewen2005 />
*{{Flag|Georgia}}<ref name=":0" />
* {{flag|Ghana}}<ref name=ewen2005 /> M16A2<ref name="NMAA"/>
* {{flag|Greece}}<ref name=ewen2005 /> M16A2/A3/A4/M4/A2E M4 is used by the Special Forces of the Hellenic Army, {{wipe|Hellenic Air Force}} and the Hellenic Navy.<ref name= hamanual/>
* {{flag|Grenada}}<ref name=ewen2005 />
* {{flag|Guatemala}}<ref name=worldpolicy2000 /> M16A1/M16A2
* {{flag|Haiti}}<ref name=worldpolicy2000 />
*{{Flag|Hungary}}<ref name=":0" />
* {{flag|Honduras}}<ref name=gander1995>Gander, Terry J.; Hogg, Ian V. ''Jane's Infantry Weapons 1995/1996''. Jane's Information Group; 21 edition (May 1995). {{ISBN|978-0-7106-1241-0}}.</ref> M16A1
* {{flag|India}}<ref name=ewen2005 />
* {{flag|Indonesia}}<ref name=ewen2005 /> M16A1
* {{flag|Iraq}}<ref>{{Cite news |url=http://news.bbc.co.uk/2/hi/middle_east/6665759.stm |work=BBC News |title=First steps to arming Iraq's soldiers |date=18 May 2007 |access-date=12 May 2010 |archive-url=https://web.archive.org/web/20121111233436/http://news.bbc.co.uk/2/hi/middle_east/6665759.stm |archive-date=11 November 2012 |url-status=live}}</ref> M16A2/A4.
** {{Flag|Kurdistan}}<ref>{{cite web |url=https://www.defensenews.com/land/2017/04/19/state-oks-humvees-howitzers-for-iraqi-peshmerga-in-isis-fight/ |work=defensenews |title=State OKs Humvees, howitzers for Iraqi peshmerga in ISIS fight |date=19 April 2017}}</ref> M16A4
* {{flag|Israel}} M16A1/M16A2E3
* {{Flag|Italy}}<ref name=":0" />
* {{flag|Ivory Coast}}<ref>{{cite book|title=Identifier les sources d'approvisionnement: Les munitions de petit calibre en Côte d'Ivoire|url=http://www.smallarmssurvey.org/fileadmin/docs/C-Special-reports/SAS-SR21-CotedIvoire-FR.pdf|first=Holger|last=Anders|date=June 2014|publisher=[[Organization:Small Arms Survey|Small Arms Survey]] and United Nations Operation in Côte d'Ivoire|isbn=978-2-940-548-05-7|page=15|language=fr|access-date=5 September 2018|archive-url=https://web.archive.org/web/20181009093415/http://www.smallarmssurvey.org/fileadmin/docs/C-Special-reports/SAS-SR21-CotedIvoire-FR.pdf|archive-date=9 October 2018|url-status=dead}}</ref>
* {{flag|Jamaica}}<ref name="ewen2005" />
* {{flag|Japan}}: M16A1 is used by Western Army Infantry Regiment along with [[Engineering:Howa Type 89|Howa Type 89]] rifles.<ref name="SAT Structure">{{cite web |archive-url=https://web.archive.org/web/20131104200548/http://www.kjclub.com/jp/exchange/photo/read.php?tname=exc_board_53&uid=5386&fid=5386&thread=1000000&idx=1&page=1&number=4103 |archive-date=4 November 2013 |script-title=ja:日本の特殊部隊 |url=http://www.kjclub.com/jp/exchange/photo/read.php?tname=exc_board_53&uid=5386&fid=5386&thread=1000000&idx=1&page=1&number=4103 |language=ja |url-status=dead}}</ref>
* {{flag|Jordan}}<ref name="ewen2005" /> M16A1/A2
* {{Flag|Kenya}}<ref name=":0" />
* {{flag|Kuwait}}<ref>{{cite web|url=https://sites.google.com/site/worldinventory/wiw_me_kuwait|title=wiw_me_kuwait – worldinventory|website=sites.google.com}} </ref> M16A1/A2
* {{flag|Latvia}}:<ref>{{cite web|url=https://sites.google.com/site/worldinventory/wiw_eu_latvia|title=wiw_eu_latvia – worldinventory|website=sites.google.com|access-date=15 January 2018|archive-url=https://web.archive.org/web/20161124202703/https://sites.google.com/site/worldinventory/wiw_eu_latvia|archive-date=24 November 2016|url-status=live}}</ref>
* {{flag|Lebanon}}<ref name=worldpolicy2000 /> M16A1<ref name=mcnab2002>{{cite book |last=McNab |first=Chris |title=20th Century Military Uniforms |year=2002 |edition=2nd |publisher=Grange Books |location=Kent |isbn=978-1-84013-476-6|page=174}}</ref>/A2/A4
* {{flag|Lesotho}}<ref name=ewen2005 />
* {{flag|Liberia}}<ref name=worldpolicy2000 /> M16A1/A2
* {{flag|Lithuania}}: Lithuanian Armed Forces<ref>{{cite web |url=http://kariuomene.kam.lt/lt/ginkluote_ir_karine_technika/automatiniai_sautuvai/automatinis_sautuvas_m-16.html |title=Lietuvos kariuomenė :: Ginkluotė ir karinė technika »Automatiniai šautuvai» Automatinis šautuvas M-16 |publisher=Kariuomene.kam.lt |date=17 April 2009 |access-date=22 August 2010 |language=lt |archive-url=https://web.archive.org/web/20100328132948/http://kariuomene.kam.lt/lt/ginkluote_ir_karine_technika/automatiniai_sautuvai/automatinis_sautuvas_m-16.html |archive-date=28 March 2010 |url-status=live}}</ref>
* {{flag|Malaysia}}<ref name=ewen2005 /> Malaysian Armed Forces, Royal Johor Military Force, Royal Malaysia Police, Malaysian Maritime Enforcement Agency and RELA Corps.
* {{flag|Mexico}}:<ref name=ewen2005 /> M16A2 is used by the Mexican Marines in the Mexican Drug War.<ref>{{Cite web|url=http://www.sadefensejournal.com/wp/mexican-drug-war-fighters/|title=Mexican Drug War Fighters|website=Small Arms Defense Journal|language=en-US|access-date=7 February 2020}}</ref>
* {{flag|Monaco}}: ''Compagnie des Carabiniers du Prince''<ref>{{cite news |url=http://ireport.cnn.com/docs/DOC-701167?ref=feeds%2Foncnn |work=CNN |title=Recession? What Recession? – CNN iReport |url-status=dead |archive-url=https://web.archive.org/web/20160101074135/http://ireport.cnn.com/docs/DOC-701167?ref=feeds%2Foncnn |archive-date=1 January 2016}}</ref>
* {{Flag|Mongolia}}<ref name=":0" />
* {{flag|Morocco}}<ref name=ewen2005 /> M16A1/M16A2/M16A3/M16A4
* {{flag|Myanmar}}: M16S1s made by Chartered Industries of Singapore provided secretly in violation of license agreements with Colt.<ref>
{{cite magazine |last=Ashton |first=William |date=1 March 1998 |title=Burma receives advances from its silent suitors in Singapore |url= |magazine=Jane's Intelligence Review |location= |publisher= |volume=10 |issue=3 |page= 3298}}</ref>
* {{flag|Nepal}}<ref>{{Cite news |url=http://news.bbc.co.uk/2/hi/south_asia/2631939.stm |work=BBC News |title=Nepal takes delivery of US rifles |date=6 January 2003 |access-date=12 May 2010 |first=Sushil |last=Sharma |archive-url=https://web.archive.org/web/20130922192502/http://news.bbc.co.uk/2/hi/south_asia/2631939.stm |archive-date=22 September 2013 |url-status=live}}</ref> M16A2 and M16A4; captured M16A2 were also used by Maoist rebels of the People's Liberation Army, Nepal during the Nepalese Civil War.<ref name="Nepal">{{cite journal|title=Legacies of War in the Company of Peace: Firearms in Nepal|journal=Nepal Issue Brief|issue=2|date=May 2013|url=http://www.smallarmssurvey.org/fileadmin/docs/G-Issue-briefs/NAVA-IB2-Legacies-of-War.pdf|pages=5–7|publisher=[[Organization:Small Arms Survey|Small Arms Survey]]|access-date=8 January 2019|archive-url=https://web.archive.org/web/20140708052928/http://www.smallarmssurvey.org/fileadmin/docs/G-Issue-briefs/NAVA-IB2-Legacies-of-War.pdf|archive-date=8 July 2014|url-status=dead}}</ref>
* {{flag|Netherlands}}: C7 and C8 variants are used by the Military of the Netherlands and LSW is used by Netherlands Marine Corps.<ref name=miller2001 /><ref>{{cite book |author1=Bartocci, Christopher R.|date=2004|title=Black Rifle II The M16 into the 21st Century|publisher=Collector Grade Publications Incorporated |isbn=0-88935-348-4}}</ref>
*{{flag|Nicaragua}}: Used by the National Police of Nicaragua and army.<ref>{{Cite web|url=https://havanatimes.org/news/ortegas-nicaraguan-police-train-for-a-civil-war/|title = Ortega's Nicaraguan Police Train for a Civil War|date = 6 January 2019}}</ref>
*{{flag|Nigeria}}<ref name="ewen2005" />
* {{flag|North Korea}}: M16A1 (probably unlicensed copies) used by KPA special forces. Used during the Gangneung incident in 1996.<ref>{{Cite news|date=25 September 1996|title=A Weapon Displayed From North Korea Special Forces and their Submarine|work=MBC News|url=http://imnews.imbc.com/20dbnews/history/1996/2001702_13448.html|url-status=live|access-date=3 June 2019|archive-url=https://web.archive.org/web/20181020071905/http://imnews.imbc.com/20dbnews/history/1996/2001702_13448.html|archive-date=20 October 2018}}</ref><ref>{{cite web|date=16 April 2013|title=Equipment of North Korean Special Forces and Espionage|url=http://bemil.chosun.com/nbrd/gallery/view.html?b_bbs_id=10044&pn=1&num=177361|url-status=live|archive-url=https://web.archive.org/web/20150524023732/http://bemil.chosun.com/nbrd/gallery/view.html?b_bbs_id=10044&pn=1&num=177361|archive-date=24 May 2015|access-date=3 June 2019|work=Yu Yong-won's Military World, Chosun Ilbo}}</ref>
* {{flag|Oman}}<ref name=ewen2005 /> M16A1
* {{flag|Pakistan}}<ref name=ewen2005 /> M16A1
* {{flag|Palestinian Authority}}: Used by Palestinian Security Forces<ref>{{cite web |author=Adnan Abu Amer |url=http://www.al-monitor.com/pulse/originals/2015/05/palestine-gaza-security-services-annual-budget-finance-aman.html |title=Security services drain Palestine's budget |publisher=Al-Monitor |date=10 May 2015 |access-date=8 June 2017 |url-status=dead |archive-url=https://web.archive.org/web/20170505024245/http://www.al-monitor.com/pulse/originals/2015/05/palestine-gaza-security-services-annual-budget-finance-aman.html |archive-date=5 May 2017}}</ref> and various local militant forces.<ref>{{cite news|url=http://news.bbc.co.uk/2/hi/in_pictures/6121208.stm|title=In pictures: Gaza offensive|work=BBC News|date=6 November 2006|access-date=20 March 2018|archive-url=https://web.archive.org/web/20180320231201/http://news.bbc.co.uk/2/hi/in_pictures/6121208.stm|archive-date=20 March 2018|url-status=live}}</ref><ref>{{cite web|url=https://www.worthynews.com/3354-hamas-fighting-with-weapons-from-israel-investigation|title=Hamas Fighting With Weapons From Israel (Investigation)|date=6 January 2009|access-date=20 March 2018|archive-url=https://web.archive.org/web/20180320230451/https://www.worthynews.com/3354-hamas-fighting-with-weapons-from-israel-investigation|archive-date=20 March 2018|url-status=live}}</ref>
* {{flag|Panama}}<ref name=ewen2005 /> M16A1.
* {{flag|Papua New Guinea}}<ref name=Capie>{{cite book|last=Capie|first=David |title=Under the Gun: The Small Arms Challenge in the Pacific|date=2004|pages=63–65|publisher=Victoria University Press|location=Wellington|isbn=978-0-86473-453-2}}</ref> M16A2
** {{flag|Bougainville}}: Used by Bougainville Revolutionary Army. Captured from Papua New Guinea Defence Force.<ref>{{Cite web|url=http://www.defence.gov.au/ADC/Publications/documents/IndoPac/2014/Ellwood_dec14.pdf|title=Indo-Pacific Strategic Papers: Understanding the neighbourhood: Bougainville's referendum for independence|last=Ellwood|first=Justin|website=Australian Department of Defense|pages=5, 19|archive-url=https://web.archive.org/web/20180324224443/http://www.defence.gov.au/ADC/Publications/documents/IndoPac/2014/Ellwood_dec14.pdf|archive-date=24 March 2018|url-status=live}}</ref>
* {{flag|Peru}}<ref name=ewen2005 /> M16A2. M16A1 Used by Navy Special Operation Forces,<ref>{{Cite web |last1=Issue |last2=V3N3 |last3=Volume 3 |title=Peruvian Small Arms: Gunning for the Shining Path – Small Arms Defense Journal |url=https://sadefensejournal.com/peruvian-small-arms-gunning-for-the-shining-path/ |access-date=26 October 2022 |language=en-US}}</ref> and by Directorate of Special Operations of the national police<ref>{{Cite web |date=29 May 2016 |title=wiw_sa_peru - worldinventory |url=https://sites.google.com/site/worldinventory/wiw_sa_peru |archive-url=https://web.archive.org/web/20160529045615/https://sites.google.com/site/worldinventory/wiw_sa_peru |archive-date=29 May 2016 |access-date=26 October 2022 }}</ref>
* {{flag|Philippines}}: Manufactured under license by Elisco Tool and Manufacturing.<ref name=ewen2005 /> M16A1s and M653Ps in use. Supplemented in Special Forces by the M4 carbine.
* {{PRT}}: A small number of M16A2s are used by the Special Actions Detachment of the Portuguese Navy.<ref>{{Cite web|title=O DESTACAMENTO DE ACÇÕES ESPECIAIS {{!}} Operacional|url=http://www.operacional.pt/o-destacamento-de-accoes-especiais/|access-date=1 July 2020|language=pt-PT}}</ref>
* {{flag|Qatar}}<ref name=ewen2005 /> M16A1.
* {{Flag|Romania}}<ref name=":0" /> M16A2<ref name="DSPI/DIR">{{cite web |url=http://www.presamil.ro/OM/2004/20/pag%2014.htm |title=Menirea Intervenției Rapide |language=ro |publisher=Presa Militara Romana |date=2004 |url-status=dead |archive-url=https://web.archive.org/web/20090408033753/http://www.presamil.ro/OM/2004/20/pag%2014.htm |archive-date=April 8, 2009 }}</ref>
* {{flag|Senegal}}: M16A1 and M16A2<ref name="NMAA">{{cite web|first1=Jeremy |last1=Binnie|first2=Erwan|last2= de Cherisey|archive-url=https://web.archive.org/web/20170622123315/http://www.janes.com/images/assets/520/71520/New-model_African_armies.pdf|title= New-model African armies|publisher= Jane's|date= 2017|archive-date= 22 June 2017|url=http://www.janes.com/images/assets/520/71520/New-model_African_armies.pdf}}</ref>
* {{Flag|Serbia}}<ref name=":0" />
* {{flag|Sierra Leone}}: 1,000+ M16A1s in use<ref>{{cite web|title=World Infantry Weapons: Sierra Leone|archive-url=https://web.archive.org/web/20161124203938/https://sites.google.com/site/worldinventory/wiw_af_sierraleone|archive-date=24 November 2016|url=https://sites.google.com/site/worldinventory/wiw_af_sierraleone|date=2013}}{{self-published source|date=December 2018}}</ref>
* {{flag|Singapore}}: Local variant of the M16A1 (M16S1) manufactured under license by ST Kinetics.<ref name=worldpolicy2000 />
* {{flag|Somalia}}<ref name=ewen2005 />
* {{flag|South Africa}}: Used by Special Forces.<ref name=ewen2005 /> Likely received from Moroccan stocks.<ref name="Morocco-ZA">{{cite web |title=History 'lesson' of note at Arts Festival |url=http://www.knysnaplettherald.com/news/Arts--Entertainment/Entertainment/173686/History-lesson-of-note-at-Arts-Festival|location=Dammam
|publisher=Knysna-Plett Herald|date=6 October 2016|access-date=22 December 2016|archive-url=https://web.archive.org/web/20161222134619/http://www.knysnaplettherald.com/news/Arts--Entertainment/Entertainment/173686/History-lesson-of-note-at-Arts-Festival|archive-date=22 December 2016}}</ref>
* {{flag|Sri Lanka}}<ref>{{cite book |last= Smith |first= Chris |title= In the Shadow of a Cease-fire: The Impacts of Small Arms Availability and Misuse in Sri Lanka |publisher= Small Arms Survey |date= October 2003 |url= http://www.smallarmssurvey.org/fileadmin/docs/B-Occasional-papers/SAS-OP11-Sri-Lanka.pdf |series= Occasional Paper No. 11 |page= 13 |access-date= 6 September 2018 |archive-url= https://web.archive.org/web/20170705130927/http://www.smallarmssurvey.org/fileadmin/docs/B-Occasional-papers/SAS-OP11-Sri-Lanka.pdf |archive-date= 5 July 2017 |url-status= dead}}</ref>
* {{Flag|Sudan}}<ref name=":0" />
* {{Flag|Suriname}}<ref name=":0" />
* {{flag|Sweden}} A small number of M16A2s are used by the Swedish Armed Forces for familiarization training, as well as a similar number of AKMs, but they are not issued to combat units.<ref>{{cite web |author=Henrik Svensk |url=http://www.soldf.com/utlvap.html |title=M16 M16A2 Kalashnikov AK-47 – Utländska Vapensatsen |publisher=SoldF.com |language=sv |access-date=13 July 2014|quote=The foreign weapons kit was purchased in 1986 to give personnel in the Armed Forces the opportunity to get to know the weapons that usually show up in war and crisis situations|archive-url=https://web.archive.org/web/20160410075842/https://www.soldf.com/utlvap.html |archive-date=10 April 2016 |url-status=dead}}</ref> The Ak 4 and Ak 5 rifles are used by Swedish Army.
* {{flag|Taiwan}}: M16A1, as well as indigenous Type 65/65K1/65K2, Type 86 and Type 91 (with AR-18 style gas piston system).<ref>{{cite web |url= http://www.militaryfactory.com/smallarms/detail.asp |title=Colt M16A2 Assault Rifle|website=Military Factory |access-date= 23 November 2014 |archive-url= https://web.archive.org/web/20141112220614/http://www.militaryfactory.com/smallarms/detail.asp |archive-date= 12 November 2014 |url-status=live}}</ref><ref name=":0" />
* {{flag|Thailand}}<ref name=ewen2005 /> M16A1/A2/A4. A variant of XM177 replica called Type 49 carbine (ปลส.49) Used in [[Religion:South Thailand insurgency|South Thailand insurgency]].
* {{flag|Tunisia}}<ref name=ewen2005 /> M16A2/A4
* {{flag|Turkey}}<ref name=ewen2005 /> M16A1/A2/A4
* {{flag|Uganda}}<ref name=ewen2005 />
* {{flag|Ukraine}}<ref>{{cite web|url=https://mil.in.ua/uk/news/ukrayinski-syly-vykorystovuyut-kanadski-gvyntivky-diemaco-c7a1/|title=Українські сили використовують канадські гвинтівки "Diemaco C7A1"|access-date=11 November 2022|language=uk}}</ref> M16A4s<ref name="Ukraine M16">{{cite web |title=Ukrainian Army Now Issuing M16A4s | website=The Armourer's Bench| date=29 January 2023|url=https://armourersbench.com/2023/01/29/m16a4s-in-ukraine/|access-date=10 February 2023 |language=en|archiveurl=https://web.archive.org/web/20230522135622/https://armourersbench.com/2023/01/29/m16a4s-in-ukraine/|archive-date=May 22, 2023}}</ref>
* {{flag|United Arab Emirates}}<ref name=ewen2005 />
* {{flag|United Kingdom}}: One of first military customers as UK purchased first AR-15s to be used in jungle warfare in Indonesia–Malaysia confrontation.{{sfn|McNab|2002|p=243}} The [[Engineering:Colt Canada C7 and C8#C8|Colt Canada C8]] (L119A1/L119A2) variant is used by Royal Military Police Close Protection Units,<ref>{{cite web |title=Royal Military Police train for close protection |url=https://www.gov.uk/government/news/royal-military-police-train-for-close-protection |publisher=Ministry of Defence |date=7 August 2012 |access-date=20 November 2015 |archive-url=https://web.archive.org/web/20151019095153/https://www.gov.uk/government/news/royal-military-police-train-for-close-protection |archive-date=19 October 2015 |url-status=live}}</ref> the Pathfinder Group, United Kingdom Special Forces<ref>{{cite web|url=http://www.eliteukforces.info/special-air-service/weapons/c8.php|title=SAS Weapons – C8 SFW Carbine L119A1s|work=EliteUKForces.info|access-date=13 December 2012|archive-url=https://web.archive.org/web/20180519233359/http://www.eliteukforces.info/special-air-service/weapons/c8.php|archive-date=19 May 2018|url-status=dead}}</ref> and 43 Commando Fleet Protection Group Royal Marines.<ref>{{cite news |last=Ripley |first=Tim |date=4 March 2016 |title=UK Royal Marine unit ditches the SA80 for Colt C8 |url=http://www.janes.com/article/58501/uk-royal-marine-unit-ditches-the-sa80-for-colt-c8 |newspaper=IHS Jane's Defence Weekly |location=London |access-date=13 June 2016 |archive-url=https://web.archive.org/web/20160317184342/http://www.janes.com/article/58501/uk-royal-marine-unit-ditches-the-sa80-for-colt-c8 |archive-date=17 March 2016 |url-status=live}}</ref>
* {{flag|United States}}<ref>{{cite web |url=http://www.army.mil/factfiles/equipment/individual/m16.html |title=M-16 Rifle Fact File for the United States Army |publisher=Army.mil |access-date=22 August 2010 |archive-url=https://web.archive.org/web/20100825003123/http://www.army.mil/factfiles/equipment/individual/m16.html |archive-date=25 August 2010 |url-status=live}}</ref>
* {{flag|Uruguay}}<ref name=ewen2005 />
* {{flag|Vietnam}}: Obtained from South Vietnam following Vietnam War<ref>{{cite book|title=Personal firepower|first=Edward Clinton|last= Ezell|publisher=Bantam Books|year=1988|series=The Illustrated history of the Vietnam War 15|oclc=1036801376|url=https://archive.org/details/personalfirepowe00ezel|pages=152–153|isbn=9780553345490}}</ref> Over 946,000 M16s were captured in 1975 alone.{{Sfn|Rottman|2011|p=34}} XM16E1, M16A1 used.
*{{Flag|Yemen}}<ref name=":0" />
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===Non-state users===
* {{flagicon image|Flagge FDLR.svg}} Democratic Forces for the Liberation of Rwanda<ref name="FDLR">{{cite book |author=Small Arms Survey |url=http://www.smallarmssurvey.org/fileadmin/docs/A-Yearbook/2015/eng/Small-Arms-Survey-2015-Highlights-EN.pdf |title=Small Arms Survey 2015: weapons and the world |publisher={{wipe|Cambridge University Press}} |year=2015 |page=201 |chapter=Waning Cohesion: The Rise and Fall of the FDLR–FOCA |ref={{harvid|Small Arms Survey 2015}} |access-date=29 August 2018 |chapter-url=http://www.smallarmssurvey.org/fileadmin/docs/A-Yearbook/2015/eng/Small-Arms-Survey-2015-Chapter-07-EN.pdf |archive-url=https://web.archive.org/web/20200803154955/https://www.smallarmssurvey.org/fileadmin/docs/A-Yearbook/2015/eng/Small-Arms-Survey-2015-Chapter-07-EN.pdf |archive-date=3 August 2020 |url-status=dead}}</ref>
* {{flagicon image|Flag of Eastern Indonesian Mujahideen (Mujahidin Indonesia Timur).svg}} East Indonesia Mujahideen<ref name="MIT">{{cite web|url=https://www.merdeka.com/peristiwa/kronologi-terduga-santoso-ditembak-mati-di-poso.html|title=Kronologi terduga Santoso ditembak mati di Poso|website=merdeka.com|date=19 July 2016|access-date=22 May 2021|language=id|archiveurl=https://web.archive.org/web/20230621035200/https://www.merdeka.com/peristiwa/kronologi-terduga-santoso-ditembak-mati-di-poso.html|archive-date=June 21, 2023}}</ref>
* {{flagicon image|Morning Star flag.svg}} Free Papua Movement<ref>{{cite web|url=https://kabarpapua.co/5-senjata-api-laras-panjang-ditemukan-dari-2-orang-kelompok-teroris-papua/|title=5 Senjata Api Laras Panjang Ditemukan dari 2 Orang Kelompok Teroris Papua|website=kabarpapua.co|date=7 September 2021|access-date=3 April 2022|language=id|archiveurl=https://web.archive.org/web/20230620201316/https://kabarpapua.co/5-senjata-api-laras-panjang-ditemukan-dari-2-orang-kelompok-teroris-papua/|archive-date=June 20, 2023}}</ref>
* {{Flag|ISIL}}<ref>{{Cite web|url=http://counterterrorismethics.com/the-past-present-and-future-weapon-use-of-isil/|title=Terrorist Group: ISIS Weapons Use &#124; Counter-Terrorism Ethics|archive-url=https://web.archive.org/web/20180426160054/https://counterterrorismethics.com/the-past-present-and-future-weapon-use-of-isil/|archive-date= 26 April 2018}}</ref><ref>{{Cite web|url=https://www.nbcnews.com/storyline/isis-uncovered/isis-shows-u-s--made-weapons-n419371|title = ISIS Shows off Its American-Made M16 Rifles|website = NBC News| date=September 2015 |archiveurl=https://web.archive.org/web/20230621035158/https://www.nbcnews.com/storyline/isis-uncovered/isis-shows-u-s--made-weapons-n419371|archive-date=June 21, 2023}}</ref>
**Bangsamoro Islamic Freedom Fighters<ref>{{Cite web|url=https://newsinfo.inquirer.net/1367153/govt-troops-recover-high-powered-guns-in-maguindanao-clash|title=Gov't troops recover high-powered guns in Maguindanao clash|date=2 December 2020|archiveurl=https://web.archive.org/web/20230620181939/https://newsinfo.inquirer.net/1367153/govt-troops-recover-high-powered-guns-in-maguindanao-clash|archive-date=June 20, 2023}}</ref>
**Maute Group<ref>{{Cite web|url=https://newsinfo.inquirer.net/1064235/pnp-afp-to-probe-possible-military-weapons-theft|title = PNP, AFP to probe possible military weapons theft|date = 18 December 2018|archiveurl=https://web.archive.org/web/20230620233840/https://newsinfo.inquirer.net/1064235/pnp-afp-to-probe-possible-military-weapons-theft|archive-date=June 20, 2023}}</ref>
*{{flagicon image|Flag of Kurdistan Workers' Party.svg}} Kurdistan Workers' Party<ref>{{Cite web|title=PKK'lı terörist, ABD yapımı silah ile yakalandı|url=https://www.meydannet.com/haber/pkkli-terorist-abd-yapimi-silah-ile-yakalandi-31735.html|archive-url=https://web.archive.org/web/20210807115457/https://www.meydannet.com/haber/pkkli-terorist-abd-yapimi-silah-ile-yakalandi-31735.html|access-date=7 August 2021|archive-date=7 August 2021|website=MeydanNet.com|language=tr}}</ref><ref>{{Cite web|title=Siirt'te PKK'lı Teröristlere Ait Silah ve Mühimmat Ele Geçirildi|url=https://icisleri.gov.tr/siirtte-pkkli-teroristlere-ait-silah-ve-muhimmat-ele-gecirildi|access-date=7 August 2021|website=icisleri.gov.tr|archiveurl=https://web.archive.org/web/20230622193035/https://icisleri.gov.tr/siirtte-pkkli-teroristlere-ait-silah-ve-muhimmat-ele-gecirildi|archive-date=June 22, 2023}}</ref>
*{{flagicon image|}} New People's Army: Captured from AFP and PNP, supplied by sympathizers, or purchased from the black market.<ref>{{cite news|title=Army destroys firearms captured [from] NPA rebs in NorthMin|url=https://www.mindanews.com/top-stories/2018/08/army-destroys-firearms-captured-form-npa-rebs-in-northmin/|access-date=20 November 2020|work=Minda News|date=23 August 2018|archiveurl=https://web.archive.org/web/20230622193034/https://www.mindanews.com/top-stories/2018/08/army-destroys-firearms-captured-form-npa-rebs-in-northmin/|archive-date=June 22, 2023}}</ref><ref>{{cite news|title=NPA killed, high-powered firearms captured in ZamBo Norte clash|url=https://www.kalinawnews.com/npa-killed-high-powered-firearms-captured-in-zambo-norte-clash/|access-date=20 November 2020|work=Kalinaw News|date=11 July 2020|archive-date=22 October 2020|archive-url=https://web.archive.org/web/20201022234754/https://www.kalinawnews.com/npa-killed-high-powered-firearms-captured-in-zambo-norte-clash/|url-status=dead}}</ref><ref>{{cite news |title=Soldiers recover NPA weapons, nab suspected rebel in NegOcc|url=https://www.pna.gov.ph/articles/1116019|access-date=20 November 2020|work=Philippine News Agency|date=20 September 2020|archiveurl=https://web.archive.org/web/20230620181932/https://www.pna.gov.ph/articles/1116019|archive-date=June 20, 2023}}</ref>
* [[File:FNL_Flag.svg|22px]] Viet Cong: Captured from U.S. and ARVN forces.<ref>{{Cite web|last=Laemlein|first=Tom|title=Guns of the Tet Offensive|url=https://www.americanrifleman.org/articles/2018/1/30/guns-of-the-tet-offensive|website=American Rifleman|archiveurl=https://web.archive.org/web/20180301154204/https://www.americanrifleman.org/articles/2018/1/30/guns-of-the-tet-offensive/|archive-date=March 1, 2018}}</ref>

===Former users===
* {{flagicon image|Flag of Afghanistan (2013–2021).svg}} [[Place:Islamic Republic of Afghanistan|Islamic Republic of Afghanistan]]: Standard issue rifle of the Afghan National Army.<ref>{{cite web|title=Afghan National Security Forces Order of Battle|url=http://www.longwarjournal.org/multimedia/ANSF%20OOBpage4-ANA.pdf|website=Long War Journal|access-date=3 November 2011|archive-url=https://web.archive.org/web/20120607171044/http://www.longwarjournal.org/multimedia/ANSF%20OOBpage4-ANA.pdf|archive-date=7 June 2012|url-status=live}}</ref> Colt Canada C7 variants also saw limited service.
* {{Flag|Australia}}<ref>{{cite web |url=http://www.diggerhistory.info/pages-weapons/allied_recent.htm |title=Australian weapons, Viet Nam and since |publisher=Diggerhistory.info |date=11 November 2002 |access-date=22 August 2010 |url-status=dead |archive-url=https://web.archive.org/web/20100811081556/http://www.diggerhistory.info/pages-weapons/allied_recent.htm |archive-date=11 August 2010}}</ref> M16A1 introduced during the Vietnam War and replaced by the [[Engineering:Steyr AUG|F88 Austeyr]] in 1989.
* {{flagicon image|MNLF_flag.svg}} Bangsamoro Republik
* {{flagicon image|Flag_of_the_FARC-EP.svg|22px}} FARC<ref>{{Cite news|url=https://www.spiegel.de/international/world/farc-preparing-for-renewed-fighting-deep-in-colombian-jungle-a-1286296.html|title = FARC Preparing for Renewed Fighting Deep in Colombian Jungle|newspaper = Der Spiegel|date = 23 September 2019|last1 = Moreno|first1 = Juan|archiveurl=https://web.archive.org/web/20230620201315/https://www.spiegel.de/international/world/farc-preparing-for-renewed-fighting-deep-in-colombian-jungle-a-1286296.html|archive-date=June 20, 2023}}</ref>
* {{flagicon image|Flag of Free Aceh Movement.svg}} Free Aceh Movement<ref name="GAM">{{cite web|url=https://www.medcom.id/foto/news/8N0MxJAb-mantan-kombatan-gam-serahkan-8-senjata-ke-tni|title=Mantan Kombatan GAM Serahkan 8 Senjata ke TNI|website=medcom.id|date=4 January 2019|access-date=22 May 2021|language=id|archiveurl=https://web.archive.org/web/20230620201315/https://www.medcom.id/foto/news/8N0MxJAb-mantan-kombatan-gam-serahkan-8-senjata-ke-tni|archive-date=June 20, 2023}}</ref>
* {{flag|British Hong Kong}}: M16A2 variant. Used by the Royal Hong Kong Regiment.<ref name="RHKR_Weapon">{{cite web |title=RHKR Equipment - Weapons |url=https://www.rhkr.org/equipment/weapon.htm |publisher=The Royal Hong Kong Regiment (The Volunteers) Association |website=www.rhkr.org |access-date=16 June 2021 |archive-url=https://web.archive.org/web/20210624195603/https://www.rhkr.org/equipment/weapon.htm |archive-date=24 June 2021 |url-status=bot: unknown }}</ref>
* {{flagcountry|Kingdom of Laos}}: Received from the US government during the Vietnam War and Laotian Civil War.<ref>{{cite book|title=The War in Laos 1960–75|series=Men-at-Arms 217|first=Kenneth |last=Conboy|date=23 November 1989 |publisher=Osprey Publishing|isbn=9780850459388|page=15}}</ref>
* {{flagicon image|Flag_of_the_Moro_Islamic_Liberation_Front.svg}} Moro Islamic Liberation Front
* {{Flag|New Zealand}}<ref name="ewen2005" /> M16; replaced in 1988 by [[Engineering:Steyr AUG|Steyr AUG]], which was being replaced with a non-Colt M16 variant in 2016.<ref>{{cite web|date=18 August 2015|title=New Zealand Army Selects LMT To Replace Steyr AUG – The Firearm Blog|url=http://www.thefirearmblog.com/blog/2015/08/18/new-zealand-army-selects-lmt-to-produce-rifle-to-replace-steyr-aug/|url-status=live|archive-url=https://web.archive.org/web/20180124093242/http://www.thefirearmblog.com/blog/2015/08/18/new-zealand-army-selects-lmt-to-produce-rifle-to-replace-steyr-aug|archive-date=24 January 2018|access-date=16 January 2018|website=Thefirearmblog.com}}</ref>
* [[File:Provisional Irish Republican Army Badge.svg|20px]] Provisional IRA – received a number of M16s during The Troubles in Northern Ireland.<ref>{{cite web|date=9 July 2015|title=The Reorganisation of the IRA in the Early 1970s|url=https://ansionnachfionn.com/2015/07/09/the-reorganisation-of-the-ira-in-the-early-1970s/|publisher=An Sionnach Fionn}}</ref>
* {{flag|Rhodesia}}: M16A1<ref name=Moorcraft>{{cite book |title=The Rhodesian War: A Military History |last1=Moorcraft |first1=Paul L. |last2=McLaughlin |first2=Peter |author-link2=Peter McLaughlin |date=April 2008 |orig-year=1982 |location=Barnsley |publisher=Pen and Sword Books |isbn=978-1-84415-694-8}}</ref>
* {{Flag|South Vietnam}}: 6,000 M16 and 938,000 M16A1, 1966–1975<ref>Walter, John, [https://archive.org/details/riflesofworld0000walt/mode/2up Rifles of the World], Krause Publications, 1998, illustrated third edition, {{ISBN|0-89689-241-7}}, p. 321</ref>
* {{flag|Zaire}}{{sfn|Rottman|2011|p=34}}<ref name= 'FDLR'/>

==Conflicts==

===1960s===
*Vietnam War (1955–1975)
*Laotian Civil War (1959–1975)
*Indonesia–Malaysia confrontation (1963–1966)
*Dominican Civil War (1965)<ref>{{cite book|title=Power Pack: U.S. Intervention in the Dominican Republic, 1965-1966 |series=Leavenworth Papers, Number 15|last=Yates|first= Lawrence A. |date=July 1988|page= 123|publisher= United States Army Command and General Staff College|url= https://history.army.mil/html/bookshelves/resmat/dom_republic/Power_Pack-US_Intervention_Dominican_Republic_1965-1966.pdf|archiveurl=https://web.archive.org/web/20230531064257/https://history.army.mil/html/bookshelves/resmat/dom_republic/Power_Pack-US_Intervention_Dominican_Republic_1965-1966.pdf|archive-date=May 31, 2023}}</ref>
*The Troubles (Late 1960s–1998)
*Colombian conflict (1964–present)
*Rhodesian Bush War (1964–1979)
*Communist insurgency in Thailand (1965–1983)
*Cambodian Civil War (1968–1975)<ref>{{cite book|title=The War in Cambodia 1970–75|series=Men-at-Arms 209|first1=Kenneth |last1=Conboy|first2= Ken |last2=Bowra|date=15 June 1989 |isbn=9780850458510|publisher=Osprey Publishing|pages=18, 41–42}}</ref>
*Communist insurgency in Malaysia (1968–1989)
*Moro conflict (1969–2019)<ref name="Filipino">{{cite thesis|title=The Filipino Way of War: Irregular Warfare through the Centuries|first1=Fernando M. |last1=Reyeg|first2= Ned B.|last2= Marsh|date=December 2011|type=Master Thesis|publisher=[[Organization:Naval Postgraduate School|Naval Postgraduate School]]|hdl=10945/10681|pages=114}}</ref>
*Communist rebellion in the Philippines (1969–present)<ref name="Philippines">{{cite book|chapter=Captured and Counted: Illicit Weapons in Mexico and the Philippines|chapter-url=http://www.smallarmssurvey.org/fileadmin/docs/A-Yearbook/2013/en/Small-Arms-Survey-2013-Chapter-12-EN.pdf|title=Small Arms Survey 2013: Everyday Dangers|url=http://www.smallarmssurvey.org/publications/by-type/yearbook/small-arms-survey-2013.html|date=2013|first=Matt|last=Schroeder|isbn=978-1-107-04196-7|publisher={{wipe|Cambridge University Press}}|page=303|access-date=5 June 2019|archive-url=https://web.archive.org/web/20190321101456/http://www.smallarmssurvey.org/publications/by-type/yearbook/small-arms-survey-2013.html|archive-date=21 March 2019|url-status=dead}}</ref>

===1970s===
*Araguaia Guerrilla War (1972–1974)<ref name=":1">{{cite web |url=http://tropasearmas.com/guerrilha-contraguerrilha-araguaia.html |archive-url=https://web.archive.org/web/20210619002342/http://tropasearmas.com/guerrilha-contraguerrilha-araguaia.html |archive-date=19 June 2021 |title=GUERRILHA E CONTRA-GUERRILHA NO ARAGUAIA}}</ref>
*Armed resistance in Chile (1973–1990)<ref name="Guiteca2013">{{Cite web |last=Fuentes |first=Jorge |date=14 January 2013 |title=El atentado contra Pinochet que casi cambia la historia de Chile |url=https://www.guioteca.com/los-80/el-atentado-contra-pinochet-que-casi-cambia-la-historia-de-chile/ |access-date=7 October 2021 |website=Guiteca|archiveurl=https://web.archive.org/web/20230520031932/https://www.guioteca.com/los-80/el-atentado-contra-pinochet-que-casi-cambia-la-historia-de-chile/|archive-date=May 20, 2023}}</ref>
*Yom Kippur War (1973)
*Lebanese Civil War (1975–1990)
*East Timor conflict (1975-1999)
*Insurgency in Aceh (1976–2005)
*Shaba II (1978)<ref name="Congo">{{cite magazine|title=Les armes de Kolwezi|first=Jacques|last=Sicard|pages=25–30|magazine=La Gazette des armes|language=fr|url=http://fr.1001mags.com/parution/gazette-des-armes/numero-111-novembre-1982/page-28-29-texte-integral|issue=111|date=November 1982|access-date=18 October 2018|archive-url=https://web.archive.org/web/20181019075744/http://fr.1001mags.com/parution/gazette-des-armes/numero-111-novembre-1982/page-28-29-texte-integral|archive-date=19 October 2018|url-status=live}}</ref>
*Cambodian–Vietnamese War (1978–1989)
*Salvadoran Civil War (1979–1992)
*Sino-Vietnamese War<ref name="浴火重生——对越自卫反击战对我国轻武器发展的影响">{{cite web|title=浴火重生——对越自卫反击战对我国轻武器发展的影响|url= https://m.fx361.com/news/2014/0923/3130795.html |date=23 September 2014|access-date=11 November 2022|archiveurl=https://web.archive.org/web/20230605042836/https://m.fx361.com/news/2014/0923/3130795.html|archive-date=June 5, 2023}}</ref>
*Sino-Vietnamese conflicts (1979–1991)
*[[Religion:Soviet–Afghan War|Soviet–Afghan War (1979–1989)]]<ref>{{cite web|url=https://pikabu.ru/story/sovetskie_soldatyi_v_afgane_s_trofeynyimi_m16_80e_4646661|title=Советские солдаты в Афгане с трофейными M-16, 80-е.⁠⁠|date=27 November 2016 |access-date=11 November 2022|language=ru|archiveurl=https://web.archive.org/web/20161129094934/https://pikabu.ru/story/sovetskie_soldatyi_v_afgane_s_trofeynyimi_m16_80e_4646661|archive-date=November 29, 2016}}</ref>

===1980s===
*Falklands War (1982)
*Sri Lankan Civil War (1983–2009)
*United States invasion of Grenada (1983)
*Thai–Laotian Border War (1987–1988)
*Bougainville Civil War (1988–1998)<ref name="Capie" />
*First Liberian Civil War (1989–1997)<ref>{{Cite book|url=https://books.google.com/books?id=SjuQ6vaH3bgC&pg=PT62|title=The Liberian Civil War|first=Mark|last=Huband|date=17 June 2013|publisher=Routledge|via=Google Books|isbn=978-1-135-25221-2|page=62}}</ref>
*United States invasion of Panama (1989–1990)

===1990s===
*Gulf War (1990–1991)
*Somali Civil War (1991–present)
*Yugoslav wars (1991–1995)
*Sierra Leone Civil War (1991–2002)<ref>{{cite book|first=Christina|last=Wille|editor1-first=Nicolas|editor1-last=Florquin|editor2-first=Eric G.|editor2-last=Berman|date=May 2005|chapter=Children Associated with Fighting Forces and Small Arms in the Mano River Union|title=Armed and Aimless: Armed Groups, Guns, and Human Security in the ECOWAS Region|chapter-url=http://www.smallarmssurvey.org/fileadmin/docs/D-Book-series/book-01-Armed-and-Aimless/SAS-Armed-Aimless-Part-1-Chapter-06.pdf|url=http://www.smallarmssurvey.org/de/publications/by-type/book-series/armed-and-aimless.html|publisher=[[Organization:Small Arms Survey|Small Arms Survey]]|isbn=2-8288-0063-6|page=197|access-date=30 January 2019|archive-url=https://web.archive.org/web/20190131040219/http://www.smallarmssurvey.org/de/publications/by-type/book-series/armed-and-aimless.html|archive-date=31 January 2019|url-status=dead}}</ref>
*Burundian Civil War (1993–2005)
*Cenepa War (1995)
*Nepalese Civil War (1996–2006)
*First Congo War (1996–1997)<ref name ='SAS 2005'/>
*Second Liberian Civil War (1999–2003)<ref>{{Cite web|url=https://www.un.org/disarmament/update/20150325/|title=Assistance to Liberia in Marking Small Arms|date=25 May 2015|website=United Nations Office for Disarmament Affairs|publisher=United Nations|access-date=10 June 2022|archiveurl=https://web.archive.org/web/20220422013918/https://www.un.org/disarmament/update/20150325/|archive-date=April 22, 2022}}</ref><ref>{{Cite web|url=https://www.hrw.org/legacy/backgrounder/africa/liberia0905/6.htm|title=Liberia at a Crossroads:Human Rights Challenges for the New Government, Reintegration of Ex-Combatants|date=September 2005|publisher=Human Rights Watch|access-date=10 June 2022|archiveurl=https://web.archive.org/web/20220611035232/https://www.hrw.org/legacy/backgrounder/africa/liberia0905/6.htm|archive-date=June 11, 2022}}</ref>

===2000s===
*War in Afghanistan (2001–2021)
*War in Darfur (2003–present)<ref>{{cite book|title=Under Attack and Above Scrutiny? Arms and Ammunition Diversion from Peacekeepers in Sudan and South Sudan, 2002–14|url=http://www.smallarmssurveysudan.org/fileadmin/docs/working-papers/HSBA-WP37-Peacekeeper-Diversions.pdf|first1=Eric G.|last1=Berman|first2=Mihaela|last2=Racovita|date=July 2015|isbn=978-2-940548-11-8|publisher=[[Organization:Small Arms Survey|Small Arms Survey]]|series=HSBA Working Paper 37|pages=69–70|access-date=7 February 2019|archive-url=https://web.archive.org/web/20160610103342/http://www.smallarmssurveysudan.org/fileadmin/docs/working-papers/HSBA-WP37-Peacekeeper-Diversions.pdf|archive-date=10 June 2016|url-status=live}}</ref>
*Iraq War (2003–2011)
*[[Religion:South Thailand insurgency|South Thailand insurgency]] (2004–present)
*Kivu conflict (2004–present)
*Insurgency in Paraguay (2005–present)<ref>{{Cite web|title=EPP mata a dos policías al atacar una subcomisaría de Horqueta, anoche - Articulos - ABC Color|url=https://www.abc.com.py/articulos/epp-mata-a-dos-policias-al-atacar-una-subcomisaria-de-horqueta-anoche-311266.html|access-date=7 May 2021|website=www.abc.com.py|language=es|archiveurl=https://web.archive.org/web/20221006144229/https://www.abc.com.py/articulos/epp-mata-a-dos-policias-al-atacar-una-subcomisaria-de-horqueta-anoche-311266.html|archive-date=October 6, 2022}}</ref>
*2006 Lebanon War
*Mexican drug war (2006–present)
*2007 Lebanon conflict (2007)
*Cambodian–Thai border dispute (2008–2011)

===2010s===
*Militias-Comando Vermelho conflict (2010–present)<ref>{{Cite web |date=4 October 2017 |title=Recent images of Rio's drug war - |url=https://www.thefirearmblog.com/blog/2017/10/04/recent-images-rios-drug-war/ |access-date=27 October 2022 |website=The Firearm Blog |language=en-US|archiveurl=https://web.archive.org/web/20230213084249/https://www.thefirearmblog.com/blog/2017/10/04/recent-images-rios-drug-war/|archive-date=February 13, 2023}}</ref>
*Syrian civil war (2011–present)<ref name="CAR 2014">{{cite book|title=Islamic State Weapons in Iraq and Syria: Analysis of weapons and ammunition captured from Islamic State forces in Iraq and Syria|url=http://conflictarm.com/wp-content/uploads/2014/09/Dispatch_IS_Iraq_Syria_Weapons.pdf|date=September 2014|author=Conflict Armament Research|page=7|ref={{harvid|Conflict Armament Research 2014}}|access-date=31 August 2018|archive-url=https://web.archive.org/web/20180826202836/http://conflictarm.com/wp-content/uploads/2014/09/Dispatch_IS_Iraq_Syria_Weapons.pdf|archive-date=26 August 2018|url-status=live|}}</ref>
*Infighting in the Gulf Cartel (2011–present)
*2013 Lahad Datu standoff
*Iraqi Civil War (2014–2017){{sfn|Conflict Armament Research 2014|pp=12–13}}
*Operation Madago Raya<ref name="MIT"/>
*Battle of Marawi (2017)<ref>{{cite web|url=http://www.thefirearmblog.com/blog/2017/06/22/arming-maute-group-marawi-city/|title=Arming the Maute Group in Marawi City – The Firearm Blog|date=22 June 2017|website=The Firearm Blog.com|access-date=16 January 2018|archive-url=https://web.archive.org/web/20171114000335/http://www.thefirearmblog.com/blog/2017/06/22/arming-maute-group-marawi-city/|archive-date=14 November 2017|url-status=live}}</ref>

===2020s===
*Republican insurgency in Afghanistan (2021–present)
*2021 Beirut clashes (2021)
*Myanmar Civil War (2021–present)
*Russian invasion of Ukraine (2022–present)<ref name="Ukraine M16"/>
*2023 Israel–Hamas war (2023–present){{citation needed|date=October 2023}}

==See also==
* Adaptive Combat Rifle
* List of Colt AR-15 and M16 rifle variants
* [[Engineering:List of AR platform cartridges|List of AR platform cartridges]]
* [[Engineering:Colt 9mm SMG|Colt 9mm SMG]]
* [[Engineering:Comparison of the AK-47 and M16|Comparison of the AK-47 and M16]]
* Daewoo K2, Republic of Korea Armed Forces (South Korea) assault rifle
* Heckler & Koch HK416
* List of individual weapons of the U.S. armed forces
* [[Engineering:M203 grenade launcher|M203 40&nbsp;mm grenade launcher]]
* Norinco CQ, M16 clone developed by China
* Robinson Arms XCR
* [[Engineering:Rubber duck (military)|Rubber duck (military)]]
* T65 assault rifle, AR-15 variant developed by ROC Army
* [[Engineering:Winchester LMR|Winchester LMR]]
* Squad Designated Marksman Rifle
* SEAL Recon Rifle
* [[Engineering:Marine Scout Sniper Rifle|Marine Scout Sniper Rifle]]
* [[Engineering:List of assault rifles|List of assault rifles]]
{{Clear}}
<!-- ==Notes==
{{Reflist|group=n}}
-->

==References==
* {{cite book|first=Gordon L. |last=Rottman |title=The M16|url=https://archive.org/details/m160000rott/|date=20 December 2011|publisher=Osprey Publishing|series=Weapon 14|isbn=978-1-84908-691-2}}
{{Reflist}}

==Further reading==
{{Refbegin|30em}}
* Modern Warfare, Published by Mark Dartford, Marshall Cavendish (London) 1985
* Afonso, Aniceto and Gomes, Carlos de Matos, ''Guerra Colonial'' (2000), {{ISBN|972-46-1192-2}}
* Bartocci, Christopher R. ''Black Rifle II The M16 into the 21st Century''. Cobourg, Ontario, Canada: Collector Grade Publications Incorporated, 2004. {{ISBN|0-88935-348-4}}
* {{Cite book|first=Edward Clinton |last=Ezell |year=1984 |title=The Great Rifle Controversy: Search for the Ultimate Infantry Weapon from World War II Through Vietnam and Beyond |location=Harrisburg, Pennsylvania |publisher=Halsted Press |isbn=978-0-8117-0709-1}}
* {{Cite book|first=David R. |last=Hughes |year=1990 |title=The History and Development of the M16 Rifle and its Cartridge |location=Oceanside, California |publisher=Armory Publications|isbn=978-0-9626096-0-2}}
* Hutton, Robert, ''The .223'', Guns & Ammo Annual Edition, 1971.
* McNaugher, Thomas L. "[https://www.rand.org/pubs/papers/P6306/ Marksmanship, Mcnamara and the M16 Rifle: Organisations, Analysis and Weapons Acquisition]"
* {{Cite journal |author=M16 Rifle Review Panel |title=Report of the M16 Rifle Review Panel |date=1 June 1968 |url=https://apps.dtic.mil/sti/pdfs/ADA953110.pdf |id=ADA953110 |publisher=Chief of Staff U.S. Army |journal= |access-date=17 March 2012 |archive-date=1 August 2013 |archive-url=https://web.archive.org/web/20130801180632/http://www.dtic.mil/cgi-bin/GetTRDoc?AD=ADA953110 |url-status=live }}
* Pikula, Sam (Major), ''The ArmaLite AR-10'', 1998
* Rose, Alexander. ''American Rifle-A Biography.'' 2008; Bantam Dell Publishing. {{ISBN|978-0-553-80517-8}}.
* Urdang, Laurence, Editor in Chief. ''The Random House Dictionary of the English Language.'' 1969; Random House/New York.
* U.S. Army; Sadowski, Robert A., Editor. ''The M16A1 Rifle: Operation and Preventive Maintenance'' Enhanced, hardcover edition 2013; Skyhorse, New York, NY. {{ISBN|1616088648}}
{{Refend}}

==External links==
* [https://www.bits.de/NRANEU/others/amd-us-archive/FM23-9%2868%29.pdf Dept of Army Field Manual FM 23-9]
* [http://www.colt.com/Catalog/Military/Products/ColtM16A4Rifle.aspx Colt's Manufacturing: The M16A4 Rifle]
* [https://fnamerica.com/products/rifles/fn-m16a4/ FN M16A4 website]
* [https://web.archive.org/web/20071128025956/http://peosoldier.army.mil/factsheets/SW_IW_M16.pdf PEO Soldier M16 fact sheet]
* [https://web.archive.org/web/20220916014316/http://www.nazarian.no/images/wep/504_FM_23-9_M16.pdf Combat Training with the M16 Manual]
* {{Internet Archive short film|id=AR10_Promotion|name="The Armalite AR-10"}}
* {{Internet Archive|id=ArmyTechnicalManualforM16Rifle-Tm9-1005-249-23p|name="Army Technical Manual (for M16 rifle) – TM9-1005-249-23P"}}
* {{Internet Archive|id=DaPam750-30|name="DA Pam 750-30 1969 US Army comic book for maintenance of the M16A1 rifle"}}, artwork by Will Eisner.
* {{Internet Archive|id=OperatorsManualForM16M16a1|name="Operator's Manual for Rifle, 5.56 mm, M16; Rifle 5.56 mm, M16A1"}}
* {{Internet Archive short film|id=gov.dod.dimoc.29997|name="Rifle 5.56mm, XM16E1, Operation and Cycle of Functioning TF9-3663 (1966)"}}
* {{Internet Archive short film|id=m16a1-field-exp|name="Rifle, M16A1 – Part II – Field Expedients (1 July 1968)"}}

{{USAF Weapons}}

[[Category:Modular firearms]]

{{Sourceattribution|M16 rifle}}