M16 rifle
Introduced during the Vietnam War, as a derivative of an U.S. Air Force survival rifle, the M16, known commercially as the Armalite or AR-15, is, especially in its evolved version, the standard battle rifle of the United States and much of the world. In the U.S. military, the most common version is a shorter-barreled M4. Both versions will accept a M203 (grenade launcher) mounted below the barrel.
Its ancestor was the AR-5 survival rifle, a small folding weapon chambered for the .22 rimfire cartridge. After it was accepted by the Air Force as the MA-1, its developer, Armalite, then a subsidiary of Fairchild Industries, proposed various battle rifle designs to militaries around the world. The AR-15 design was licensed to Colt Industries.[1]
Based on patents by George Stoner, the M16 broke several traditions in American weapons design, and indeed a number of worldwide assumptions. It is defined as an assault rifle, the most important aspects of which being that it fires an intermediate-power rifle cartridge. A "full-power" rifle cartridge would be a NATO 7.62x51mm caliber used by the WWII M1 Garand, or the later M14 (rifle) and M60 (machine gun), where submachine guns and some carbines fire a pistol round, such as the 9mm or .45 ACP. 5.56x45mm rounds for the M16 are at the lower end of caliber (i.e., diameter) for a rifle cartridge, but make up for lower bullet weight by a higher muzzle velocity.
Some of the ideas that went into selecting that cartridge was the assumption that most longer-range engagements are not fought with individual rifles, but with machine guns and artillery, with long-range precision rifle fire only from specialists. The need was to fire many rounds to have the enemy take cover; there was no attempt to have "one bullet, one kill".
The smaller round let all users carry a greater number of rounds of ammunition, but also reduced the size and weight of the rifle, which made it easier for small Asians to use.
Early versions & problems
Unfortunately, the rifle was designed for a particular propelling powder charge, which was not used in the original production ammunition. This ammunition tended to foul the rifle with deposits of poweder residue. Coupled with some less than ideal metal selection of certain internal parts of the rifle, the early model M16's acquired a bad reputation for needing scrupulous maintenance — not always practical in the field — or they might jam.
In contrast, the Soviet counterpart of the time, the AK-47 firing a reduced-power 7.62mm round, was extremely tolerant to dirt and rarely jammed. To make up for the physically larger cartridges, AK-47's had larger magazines than the M16.
Meanwhile, the Armalite Company designed the AR-18 military and AR-180 commercial versions in 1963. While they were cheaper to produce, the M-16 and AK-47 had achieved dominance, and only approximately 20,000 were built.
Evolution
Over time, however, the 5.56x45mm ammunition was made to appropriate specifications, certain internal parts of the rifle were nickel-plated, and the later M-16s are reliable weapons. A machine gun, the M249 (machine gun) in U.S. service but derived from the Belgian FN Minimi (machine gun) design, fires the same 5.56x45mm ammunition and became the standard squad automatic weapon. The M249 has replaced the M60 as a squad weapon, giving the logistical advantage of having all primary individual weapons firing the same ammunition.
Armalite subsequently introduced the AR-180B, which has much greater parts interchangeability with the M-16 and AR-15.
Current versions
The U.S. Army is currently using the M16A2, as well as, the M16A4 and the M4 carbine as its Standard Issue Assault Rifle.
The U.S. Navy is currently using the M16A3 as its Standard Issue Assault Rifle.
The U.S. Marine Corps is currently using the M16A4 and the M4 carbine as its Standard Issue Assault Rifle.
The U.S. Air Force is currently using the M16A2 as its Standard Issue Assault Rifle.
The differences between the versions of these rifles is subtle.
The M16A2 has two fire modes (semi-automatic and burst mode). It was originally designed by the Marine Corps with an adjustable windage sight (rear), a longer stock, and a heavier barrel.
The M16A3 is identical to the M16A2 except that its two fire modes are semi-automatic and automatic.
The M16A4 was designed with a flat top receiver so as to easily mount different sights. In addition to the flat top it also features a Picatinny rail system for mounting different optics, flashlights, hand-grips, etc...
The M4 is a smaller version of the M16 with many of the same features. The M4, in addition to the features described above, usually features an adjustable butt-stock allowing for a number of different positions.
M203 grenade launchers, which use the same ammunition as the M79 grenade launcher, can mount underneath the barrel of an M16.