M16 rifle
The M16 rifle is a family of assault rifles adapted from the ArmaLite AR-15 rifle for the United States military. The original M16 rifle was a 5.56×45mm automatic rifle with a 20-round magazine.
In 1964, the XM16E1 entered US military service as the M16 and in the following year was deployed for jungle warfare operations during the Vietnam War. In 1969, the M16A1 replaced the M14 rifle to become the US military's standard service rifle. The M16A1 incorporated numerous modifications including a bolt-assist, chrome-plated bore, protective reinforcement around the magazine release, and revised flash hider.
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 cartridge and has a newer adjustable rear sight, case deflector, heavy barrel, improved handguard, pistol grip, and buttstock, as well as a semi-auto and three-round burst fire selector. Adopted in July 1997, the M16A4 is the fourth generation of the M16 series. It is equipped with a removable carrying handle and quad Picatinny rail for mounting optics and other ancillary devices.
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 mm caliber. The US military has largely replaced the M16 in frontline combat units with a shorter and lighter version, the M4 carbine. In April 2022, the U.S. Army selected the SIG MCX SPEAR as the winner of the Next Generation Squad Weapon Program to replace the M16/M4. The new rifle is designated M7.
History
Background
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 caliber. Largely in deference to tradition, this recommendation was ignored and the Army referred to the caliber as "full-sized" for the next 35 years. After World War II, the United States military started looking for a single automatic rifle to replace the M1 Garand, M1/M2 carbines, M1918 Browning automatic rifle, M3 "Grease Gun" and Thompson submachine gun. However, early experiments with select-fire versions of the M1 Garand proved disappointing. During the Korean War, the select-fire M2 carbine largely replaced the submachine gun in US service and became the most widely used carbine variant. However, combat experience suggested that the.30 carbine round was underpowered. American weapons designers concluded that an intermediate round was necessary, and recommended a small-caliber, high-velocity cartridge.However, senior American commanders, having faced fanatical enemies and experienced major logistical problems during World War II and the Korean War, 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 general-purpose machine gun in concurrent development. This culminated in the development of the 7.62×51 mm NATO cartridge.
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 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. The AR-10 featured an innovative straight-line barrel/stock design, forged aluminum alloy receivers, and with phenolic composite stocks. It had rugged elevated sights, an oversized aluminum flash suppressor and recoil compensator, and an adjustable gas system. 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. For a 7.62 mm NATO rifle, the AR-10 was incredibly lightweight at only empty. 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. In the end, the U.S. Army chose the T44, now named the M14 rifle, which was an improved M1 Garand with a 20-round magazine and automatic fire capability. The U.S. also adopted the M60 general-purpose machine gun. Its NATO partners adopted the FN FAL and HK G3 rifles, as well as the FN MAG and Rheinmetall MG3 GPMGs.
The first confrontations between the 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. And, while the M2 carbine offered a high rate of fire, it was under-powered and ultimately outclassed by the AK-47. 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.
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, to develop a.223-inch caliber select-fire rifle weighing when loaded with a 20-round magazine. The 5.56 mm round had to penetrate a standard U.S. helmet at and retain a velocity over the speed of sound while matching or exceeding the wounding ability of the.30 carbine cartridge.
This request ultimately resulted in ArmaLite developing a scaled-down version of the AR-10, named the AR-15. The AR-15 was first revealed by Eugene Stoner at Fort Benning in May 1957. 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 auto fire due to the reduced bolt thrust and 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.
In 1958, the Army's Combat Developments Experimentation Command ran experiments with small squads in combat situations using the M14, AR-15, and Winchester's Light Weight Military Rifle. 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. 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. 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. 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.
Throughout 1962 and 1963, the U.S. military extensively tested the AR-15. Positive evaluations emphasized its lightness, "lethality", and reliability. However, the Army Materiel Command criticized its inaccuracy and lack of penetrating power at longer ranges. 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 match grade M14s to compete against AR-15s out of the box. 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.
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. 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."
After modifications, the new redesigned rifle was subsequently adopted as the M16 Rifle:
Despite its early failures the M16 proved to be a revolutionary design and stands as the longest continuously serving rifle in US military history. It has been adopted by many US allies and the 5.56×45 mm NATO cartridge has become not only the NATO standard but "the standard assault-rifle cartridge in much of the world". It also led to the development of small-caliber high-velocity service rifles by every major army in the world. It is a benchmark against which other assault rifles are judged.