M16 (rifle)

M16 is the U.S. Military designation for a family of rifles derived from the Armalite AR-15. It is an assault rifle which fires NATO standard 5.56 mm ammunition. It has been the primary infantry rifle of the United States military since 1967, is in use by 15 NATO countries, and has been the most produced firearm in its caliber.

Design

The M16 is made of aluminum alloy and plastics, except for the steel barrel and parts of the action. Early models were especially lightweight at 3.2 kg (7.5 lb), about 30% less than older 7.62 mm "battle rifles" of the 1950s and 1960s. It also compares very favourably with the 5 kg (loaded) AK47. New models weigh more (8.5 lb or 3.9 kg) because of the "heavy" barrel used to increase accuracy. The rifle is 40 inches (1.02 m) long with standard 20 inch (508 mm) barrel. Stoner experimented with titanium barrels and receivers for even greater weight savings, but failed to achieve reliable operation at the time.

Related Topics:
Aluminum - Plastics - AK47 - Titanium

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One distinctive ergonomic feature is a plastic or metal stock directly behind the action, which contains a recoil spring that serves the dual function of operating spring and recoil buffer. The straight-back stock and spring act to reduce muzzle rise, especially during automatic fire. As a result, most users find the M16 type rifle easy to use. Because recoil does not significantly shift the point of aim, user fatigue is reduced.

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Another distinctive ergonomic feature is that the main sight is on the top of a carry handle on top of the receiver. This means that the user need not turn the head sideways to sight the rifle. The carry handle is also a popular feature. Newer models have a "flattop" upper receiver to which the user can attach either a conventional carry handle/sighting system or numerous optical devices such as night vision scopes.

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The action is gas-operated, cocked by gases from a small hole in the barrel. The M16 design has a uniquely simple "direct drive" gas system, which also saves weight. Hot gases from the barrel vent directly into the receiver to push the bolt carrier rearward, eliminating the need for a traditional operating rod and spring assembly. While this reduces the number of moving parts and results in a simpler design, authorities differ about whether the design is more reliable than earlier service rifles.

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The magazine release is on the right side of the rifle but releases are available for left-handed users. Current military magazines have 30 rounds, as opposed to the 20 round magazines issued in Vietnam. (30 round magazines were not developed and issued until late in the war.) Magazines are sometimes taped in upside-down pairs to speed reloading. Aftermarket double magazine clips are available. This practice is discouraged by military authorities because it is said to increase the chance that the top of a magazine will be damaged or pick up dirt. Nevertheless, all it takes is a quick look at recent pictures from Iraq (2004), to see that Special Forces and mainstream military forces are quick to make use of double magazine clips, as well as high-capacity magazines.

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The bullet is small in caliber, 0.224 in (contrary to the 5.56 mm designation, the actual diameter is roughly 5.7 mm). The bullet often fragments when it strikes flesh. When fired from less than 100 meters, the bullet will penetrate 100 mm (4 in) into body tissue, before rotating 90 to 180 degrees. The force of bullet being pushed through dense tissue will then cause it to break nearly in half at the cannelure, which is a groove allowing the bullet casing to be sealed to the copper jacket. The rear section of the 5.56 mm bullet will then splinter into numerous tiny pieces, causing severe damage to surrounding tissue. The combination of high velocity and a fragile small bullet is more likely to cause incapacitating injuries than death by hydrostatic shock. The relatively small bullet drifts more than heavier bullets at long ranges, but users can be trained to compensate to a degree. For this reason the M16 and variants are well suited for urban and jungle warfare, unlike previous 7.62 mm infantry small arms, which cannot be fired successfully at close ranges as rapidly or with as much volume of fire.

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The U.S. does not, generally, issue fully automatic M16-style rifles. Doctrinally, automatic fire is reserved for heavier machine guns that are designed to manage the recoil and deliver accurate fire even on fully automatic. Fully automatic fire would also expend ammunition faster, requiring soldiers to carry more to compensate. Also, the M16 barrel is too light to support sustained automatic fire and would overheat. Most M16- and M4-style weapons issued are capable of semiautomatic fire with an additional mode that utilizes a three-part automatic sear that fires three-round bursts for each pull of the trigger, providing an "optimal" tradeoff of firepower, accuracy, and ammunition conservation. Colt did develop an AR variant made with a heavier barrel, belt-feed, and fast barrel replacement, but this was canceled in favor of the M249 Squad Automatic Weapon in the 1970s. Squads are now issued the M249 (one per fireteam) to provide automatic fire. Fully automatic versions (the M16A3 and M4A1) are issued by the U.S. military to certain specialized units.

Related Topics:
Fully automatic - Semiautomatic - Sear - Trigger - M249 - Squad Automatic Weapon - M4A1

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