M16 Assault Rifle

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(From http://www.pmulcahy.com/assault_rifles/us_assault_rifles_a-c.htm)

This is the standard combat rifle of the US, as well as having been used or being used by over 50 other armies. The M-16 rivals the AK-series for widespread use. The M-16 is an effective and popular weapon, but is a bit sensitive to dirt. The M-16 was originally designed by the small arms genius Eugene Stoner, based on the AR-10’s action and a development of the .222 Remington round, which was designed to fall in range, penetration, and wounding potential somewhere between the 7.62mm NATO round and the .30 Carbine round. The US Army had expressed a desire (against the wishes of the DoD) as early as 1957 for a light rifle to replace the M-14 as its standard assault rifle, which had already proven to be too heavy for regular troop use and uncontrollable in automatic fire. The prototypes went through several iterations based upon troop and small-arms-expert evaluations. Different ammunition types also were tried, and the AR-15 (as the M-16 was called at the time by Stoner) also faced fierce opposition from the DoD’s Chief of Ordinance, who wanted to stick with the M-14. This meant that official adoption, first by the USAF, did not occur until 1962, who issued it to their security troops), and later that year, for use by SEAL and Special Forces advisors in Vietnam.

Since the SPIW program essentially produced nothing acceptable to the military, Secretary McNamara finally intervened and told the Army to accept the M-16, first for special ops, airborne, Air Cav, and air assault troops, and then later for the Army and Air Force in general. This crash program unfortunately led to quality control problems, which were only partially rectified.

The original M-16 contained most of the features which became standard on future M-16s. It uses the now-standard 20-inch length barrel, though the flash suppressor is slightly different than on later models (though still of the slotted type), and is also made of light alloy instead of the steel of later models. It has no forward assist, and the chamber and barrel are not chromed, which led to quick corrosion and fowling in Vietnam’s climate. (Air Force Security troops, for the most part not operating in such environments or in the bush, didn’t really have this problem.) At the time of issue, the M-16 was still using the IMR Ball propellant recommended by Eugene Stoner, which also greatly decreased fouling and corrosion.

The M-16A1 is perhaps the most common version of the M-16. The original M-16A1s quickly suffered from not being used with IMR Ball propellant (instead, the military decided to go with a much cheaper propellant that caused much more fouling and corrosion, and though they later changed to better-quality propellant, it still did not match the quality of the original IMR Ball propellant), a myth that sprang up among soldiers that the M-16A1 didn’t require any regular cleaning, and a barrel and chamber that corroded rapidly. Thus, the M-16A1 quickly gained a reputation of jamming, usually at the wrong moment. The problems with corrosion were largely fixed by chroming the chamber and barrel. The M-16A1 also introduced the forward assist, which is sort of plunger that can be used to fully close the bolt when the M-16A1 is fouled inside the receiver or otherwise does not seat properly. (This feature as added at the insistence of the Army and Marines; the USAF also has some M-16A1s, but most of them don’t have forward assists, and are often mistaken for original M-16s.) The T-bar charging handle was made wider, the slotted flash suppressor was changed to steel construction (and later changed to the now-familiar birdcage pattern), and the magazines were changed from steel to an aluminum alloy (including a new 30-round magazine introduced in 1969). Most of the problems experienced with the M-16A1 can be traced back to improper maintenance (personally, even though I have always cleaned my weapons thoroughly, have always had problems with extraction failures on both the M-16A1 and A2, however, as did many of my fellow soldiers). The recoil buffer had mass added, which both curbed the too-high cyclic rate and also corrected a problem where the bolt tended to literally “bounce” inside the receiver, resulting in a bolt which did not close properly. It should be noted that in addition to Colt, many M-16A1s were manufactured by GM’s Hydra-Matic division and Harrington & Richardson. (The M-16A1s built by these two alternate manufacturers actually turned out to be superior in quality to those manufactured by Colt!) The M-16A1 has turned up in some strange places; for example, leftist rebels in Nicaragua, El Salvador, and Guatemala were often encountered with it. The serial numbers on the captured M-16A1s were traced to weapons lost or abandoned in Vietnam before US involvement in that country ended. In addition, some 30+ countries are licensed to manufacture the M-16A1, so they may be encountered pretty much all over the globe.

Though the US Army was satisfied with the M-16A1, the Marines were not. In 1980, they began to tinker with the M-16A1, producing the M-16E1A1, which eventually resulted in the M-16A2, which was adopted by the Marines in 1983. Changes made for the M-16A2 included better chroming for the chamber and barrel, a change to a 1:7 rifling twist (from 1:12) to suit the superior SS-109 ammunition which had been developed by FN and Heckler & Koch, the omission of the bottom slot from the flash suppressor (allowing it to function as sort of a partial muzzle brake), and a small block added behind the ejection port to deflect hot brass away from left-handed shooters (hot brass often ends up in the shirts or face of left-handed shooters of the M-16 and M-16A1). The handguard was changed from its triangular cross-section to a round, ribbed criss section; this is not only ergonomically better, but simplifies the supply chain by eliminating the need to have left and right handguard sections. They also dissipate heat better. The pistol grip was also redesigned, with finger swells. The formerly solid polymer stock was replaced with a fiberglass/nylon composite which is filled nylon foam, which helps counteract the fact that the M-16A2 is heavier elsewhere, and is also far stronger than the original stock. The rear sight is replaced by one which allows adjustments for windage and elevation by simple dials (on the M-16A1, windage adjustments had to be made by sticking the point of a bullet or other object into holes in the adjustment dials, and elevation was done on the front post in the same manner). Perhaps the most controversial change was the fire selector; the capability for fully automatic fire was replaced with a 3-round burst feature, with a cyclic rate so high that the recoil from the first round is not felt until the third round is already out of the barrel. The barrel is the subject of more misunderstanding than anything else on the M-16A2; it is roughly double the thickness, but only at about the last third of the barrel. Many think this is to increase accuracy (untrue), to increase heat dissipation (mostly true), and to stiffen the barrel (a little bit true). However, the primary reason for this thickening is a reflection of grunt mentality; the primary reason this was done is to stop soldiers from bending the barrel when using their rifle as an ad hoc crowbar.

The US Army was originally quite reluctant to accept the M-16A2; they did not want to have to switch to SS-109 ammunition since they had mountains of old M-193, and they did not like the burst fire mechanism, as they felt that the ability to produce massive quantities of firepower increased the confidence and morale of its troops. (In essence, they were underestimating their people.) Ironically, a version of the M-16A2 was made with full-auto capabilities, but they were built only for export as the request of certain customers, and not used by the US military. However, in 1985, they were basically forced by the Pentagon to adopt the M-16A2. In addition to the full-auto M-16A2 mentioned above, other versions built for specific export customers include an M-16A2 with full auto features as well as M-16A1-type sights, and an M-16A2 with a medium-weight M-16A1-type barrel.

The M-16A3 is identical to the M-16A2 but has a removable carrying handle that is mounted on a MIL-STD-1913 (for better mounting of optics) and is without burst control. This version is the current standard version of the M-16 for the US Navy SEAL, SeaBee, and Shore Security units. The M-16A3 also restores the full-automatic feature to the M-16, in lieu of the 3-round burst feature. The M-16A4 is identical to the M-16A3 except for fire control components which uses the selector with the 3-round burst feature. This weapon is the standard issue rifle US Army and USMC combat units that do not use the M-4 and is often seen with an ACOG-type sight mounted on the rail rather than standard iron sights.

Finally, in the Iraq and Afghanistan interventions, the Army and Marines began been using specialist versions of the M-16A4; the Army calls theirs the SDM-R (Squad Designated Marksman Rifle), while the Marines call it the SAM-R (Squad Advanced Marksman Rifle). These are “semi-sniper rifles,” designed for sharpshooters assigned to squads of troops who are not trained as full snipers. The SDM-R and SAM-R use a heavy, match-quality barrel, and the carrying handle is replaced by a MIL-STD-1913 rail which extends from the receiver to the front sight post. No rear iron sights are normally used, but can be added to the rail. The front sight can also be removed as required. The barrel is 20 inches long and is free-floating, but uses a 1:8 twist to accommodate both standard SS-109 ammunition and match-quality rounds, and is made from stainless steel. The trigger and fire mechanism has been replaced by a two-stage match trigger, and the SDM-R and SAM-R are semiautomatic-only weapons. On the handguards is mounted a Harris S-L light bipod, adjustable for height and cant. The M-4-based version is identical except for the 14.5-inch barrel. The cost of these weapons below include a compact telescopic sight.

Designation Ammunition Load Magazines Barter
M-16 5.56mm NATO 3.1 kg 10, 20, 30 $606
M-16A1 5.56mm NATO 3.18 kg 10, 20, 30 $611
M-16A2 5.56mm NATO 3.4 kg 10, 20, 30 $616
M-16A3/A4 5.56mm NATO 3.43 kg 10, 20, 30 $626
M-16A4 SDM-R/SAM-R 5.56mm NATO 4.64 kg 10, 20, 30 $1305
Weapon ROF Damage Pen Bulk SS Burst Range
M-16/M-16A1 5 3 1-Nil 6 3 6 55
M-16A2/A4 3 3 1-Nil 6 2 4 55
M-16A3 5 3 1-Nil 6 2 6 55
M-16A4 SDM-R/SAM-R SA 3 1-Nil 6 2 Nil 59
With Bipod SA 3 1-Nil 6 1 Nil 77

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M16 Assault Rifle

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