Editing M16 rifle (section)

===Adoption===
[[File:M16a1m16a2m4m16a45wi.jpg|thumb|From top to bottom: [[#XM16E1 and M16A1 (Colt Model 603)|M16A1]], [[#M16A2|M16A2]], [[M4 carbine#M4A1|M4A1]], [[#M16A4|M16A4]].]]
[[File:Ricards King Cleans His M-16, 19 December 1967 (29259454721).jpg|thumb|right|A Marine of the [[3rd Battalion, 1st Marines]] cleans his XM16E1 in December 1967.]]

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 [[John F. Kennedy]] that having two different calibers within the military system at the same time would be problematic and the request was rejected.{{sfnp|Rose|2008|p=372}} In October 1961, William Godel, a senior man at the [[DARPA|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.{{sfnp|Rose|2008|pp=372–373}} [[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.{{sfnp|Bruce|2002|pp=20-27}}

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.{{sfnmp|1a1=Bruce|1y=2002|1pp=20-27|2a1=Rose|2y=2008|2p=372}} 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.{{sfnp|''AR15.com''|2008}} These wounds were so devastating that the photographs remained classified into the 1980s.{{sfnp|Rose|2008|p=373}}

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.{{sfnmp|1a1=Bruce|1y=2002|1pp=20-27|2a1=Kern|2y=2006|2p=10}} U.S. [[United States Secretary of Defense|Secretary of Defense]] [[Robert McNamara]] now had two conflicting views: the ARPA report{{sfnp|''DARPA''| 1962}} favoring the AR-15 and the Army's position favoring the M14.{{sfnp|Bruce|2002|pp=20-27}} 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.

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.{{sfnp|Bruce|2002|pp=20-27}} 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 [[Chrome plating|chrome-plated]] chamber.{{sfnmp|1a1=Defense Technical Information Center (DTIC)|1y=1968|1p=5|2a1=Sweeney|2a2=Ferguson|2y=2004|2p=240}}

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),{{sfnp|Kokalis|2010|p=2}} the newly redesigned rifle was renamed the ''Rifle, Caliber 5.56&nbsp;mm, M16''.{{sfnp|Defense Technical Information Center (DTIC)|1968|p=5}}{{sfnp|Kern|2006|p=10}} 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 [[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;{{sfnmp|1a1=Bruce|1y=2002|1pp=20-27|2a1=Rose|2y=2008|2pp=380, 392}} and to appease General LeMay, the Air Force was granted an order for another 19,000 M16s.{{sfnmp|1a1=Ezell|1a2=Pegg|1a3=Smith|1a4=Smith|1y=1993|1pp=46-47|2a1=Rose|2y=2008|2p=380}} 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.{{sfnp|Defense Technical Information Center (DTIC)|1968|p=5}}

In 1964, the Army was informed that [[DuPont]] could not mass-produce the [[Improved military rifle powder#IMR|IMR 4475]] stick powder to the specifications demanded by the M16. Therefore, [[Olin Corporation|Olin Mathieson Company]] provided a high-performance [[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).{{sfnp|Fallows|1981|pp=56-65}}

In March 1965, the Army began to issue the XM16E1 to infantry units. However, the rifle was initially delivered without adequate cleaning kits{{sfnp|Bruce|2002|pp=20-27}} 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.{{sfnp|Rottman|2011|p=20}} Furthermore, cleaning was often conducted with improper equipment, such as [[insect repellent]], water, and aircraft fuel, which induced further wear on the weapon.{{sfnp|Rottman|2011|p=24}} As a result, reports of stoppages in combat began to surface.{{sfnp|Bruce|2002|pp=20-27}} The most severe problem was known as "failure to extract"—the spent cartridge case remained lodged in the chamber after the rifle was fired.{{sfnp|Bruce|2002|pp=20-27}}{{sfnp|''The New York Times, At War Blog'', November 12, 2009}} Documented accounts of dead U.S. troops found next to disassembled rifles eventually led to a Congressional investigation:{{sfnmp|1a1=Bruce|1y=2002|1pp=20-27|2a1=Fuerbringer|2y=1967|2p=7}}

{{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.{{sfnp|Fuerbringer|1967|p=7}} }}

In February 1967, the improved XM16E1 was standardized as the M16A1.{{sfnp|Ezell|Pegg|Smith|Smith|1993|pp=46-47}} The new rifle had a chrome-plated chamber and bore to eliminate corrosion and stuck cartridges, and other minor modifications.{{sfnp|Bruce|2002|pp=20-27}} 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.{{sfnmp|1a1=Eisner|1y=1968|1p=4|2a1=Rottman|2y=2011|2p=79}} As a result, reliability problems were largely resolved and the M16A1 rifle achieved widespread acceptance by U.S. troops in Vietnam.{{sfnmp|1a1=Bruce|1y=2002|1pp=20-27|2a1=Coomer|2y=1968|2p=7}}

In 1969, the M16A1 officially replaced the M14 rifle to become the U.S. military's standard [[service rifle]].{{sfnp|Ezell|Pegg|Smith|Smith|1993|pp=746–762}}{{sfnp|Urdang|1968|p=801}} In 1970, the new WC 844 powder was introduced to reduce fouling.{{sfnp|Watters|2004|p=1}}

Colt, H&R, and GM Hydramatic Division manufactured M16A1 rifles during the Vietnam War.<ref>{{cite web |last= Iannamico|first= Frank|date= 15 December 2022|title=Forgotten M16A1 Rifle Manufacturers: GM/Hydra-Matic and Harrington & Richardson – Part I|url= https://smallarmsreview.com/forgotten-m16a1-rifle-manufacturers-part-i-gm-hydra-matic-and-harrington-richardson/|website=smallarmsreview.com |access-date= 15 April 2025}}</ref> M16s were produced by Colt until the late 1980s when FN Herstal (FN USA) began to manufacture them.{{sfnp|Rosenthal|1988|p=32}}