M16

M16 also refers to the Eagle Nebula in astronomy.

The M16 is an assault rifle which fires NATO 5.56mm ammunition. This has been the standard infantry weapon of the US Army since 1964. It is manufactured by Colt and Fabrique Nationale; with variants produced by Heckler und Koch, Knight's Armament, Bushmaster, Diemco, Panther Arms, and many other arms companies.

Table of contents

1 Operation
2 Field stripping and cleaning
3 Maintenance
4 Design
5 History and Variants

Operation

Insert the magazine. Pull the cocking lever to the rear and release. Turn the selector from "safe" to "fire". Place the stock against your shoulder, (for long distances, place your weak arm in the sling,) aim and pull the trigger.

To release the empty magazine, press the magazine-release at the right above the trigger-guard, and catch the magazine with your other hand.

Field stripping and cleaning

This weapon can be field-stripped with no tool other than a round of ammunition. The U.S. Army manual contains an optimized sequence.

[A more complete field-strip description would be good here.]

Maintenance

Basic cleaning is to swab the barrel with powder solvent until clean, followed by a swab of light oil. This is recommended after each firing session. Military ammunition often uses corrosive primers.

Keep this weapon dry. A surprising minor weakness is that the barrel can wick water up into the barrel by capillary action. In this state, the weapon can misfire, possibly injuring the user.

Design

The M16 is one of a family of related weapons designed by Eugene Stoner of Armalite Systems, formerly of Costa Mesa, California. Others include a squad automatic weapon and the AR-10, a relatively rare 7.62x51mm NATO rifle that recently returned to production.

A major goal of the design was to use (then) modern materials and manufacturing processes to make a lightweight rifle with lightweight ammunition, to replace the heavy M14 rifle that was standard issue until 1962.

The M16 is an ergonomic, angular, modernistic and unusually lightweight rifle (originally 3.2kg, compare to 5kg for an AK47). It has a pistol grip, which aids intuitive pointing. The sights allow the user to dial in the range to the target without other adjustments.

The M16 is made of aluminum and plastics, except for the steel barrel and parts of the action. Early models were especially lightweight at 3.2 kg (~7.5 lbs), about 30% less than older 7.62mm "battle rifles" of the 1950s and 1960s. New models weigh more (~8.5 lbs) because of the "heavy" barrel used to increase accuracy. The gun is 40 inches in length. Stoner experimented with Titanium barrels and receiver, but failed to achieve reliable operation.

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 direct-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. In particular, multiple-round bursts cause much less muzzle-lift, so the rifle is very controllable. Because recoil does not significantly shift the point of aim, user fatigue is reduced. This reduction in recoil coincided well with the entry of women into the Army.

Another distinctive ergonomic feature is that the main sight is in 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.

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. Maintenance can be tricky. Official authorities say that modern versions of the M16A2 with modern ammunition are very reliable.

A forward assist lever (to manually close the action in the event of a failure to feed) was omitted from the earliest models to prevent entry of dirt, but it is included on the modern models along with a spring loaded dust cover.

The bullet is small caliber, 5.56mm (.223"), and often fragments when it strikes flesh. 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.

History and Variants

It was originally developed as the Armalite AR-15 in the late 1950s and early 1960s by Eugene Stoner of Armalite Systems, formerly of Costa Mesa, California.

The AR-15 was initially adopted by the U.S. Special Forces, and later found favor with the general army. It was later produced by Colt and other makers. The total quantity produced in all models world-wide has been about 7 million.

The first revision to the M16 was minor—the replacement of the original "pronged" flash suppressor with a "birdcage" model because of complaints that the pronged version snagged on brush in Vietnam.

Early U.S. users in the Vietnam war had numerous reliability problems. Some believe that this is because those users (who had allegedly been told that the gun required very little maintenance) had neglected maintenance and the neglected guns became extremely unreliable. However, other evidence points to subtle problems with compatibility between the ammunition and the early versions of the gun, such that even perfectly maintained and cleaned guns were unreliable. The gunpowder of early version M16 ammunition was clean-burning, and the gun did not require chrome plating in the receiver area. It is widely believed that a last-minute change to the gunpowder formula was made shortly before the gun was introduced into service. While resulting in a higher muzzle velocity, it caused the weapon to foul much more quickly, and because it lacked plating, it would tend to jam.

In Vietnam, some soldiers were issued a unique version of the M16 called the XM-177 or CAR-15. The XM-177 had a shorter barrel (~26 cm) and a telescoping stock, which made it substantially more compact and significantly handier. Numerous problems with muzzle flash and loud report resulted in Colt modifying the design to produce the XM-177E1 and XM-177E2 toward the end of the Vietnam conflict. The final XM-177E2 had a 29 cm barrel with a long flash suppressor. This version became known as the "Commando" model and was issued in limited numbers to special forces, helicopter crews, Air Force pilots, officers, radio operators, artillerymen, and troops other than front line riflemen.

In early models, the selective fire control selected either single-shot, or automatic. As designed, the rate of automatic fire was about 700 rounds per minute, but a last-minute change to the gunpowder formula in the ammunition caused it to become very high, near 900 rounds per minute.

Civilian models lack selective fire capability.

The magazine release is on the right side of the rifle but can be switched for left-handed users. Current military magazines have 30 rounds, and 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.

In early models, a low-twist rifling scheme gave muzzle velocities exceeding 3200 fps, however, the bullet could tumble at long ranges. Modern rifles have a faster rifling twist, and the muzzle velocity is nearly as high, at 2900 fps or more.

After the M16A1 was adopted in the 1970s, user feedback and doctrinal changes led to the development of the M16A2, introduced in 1982.

The main impetus to a new gun was that the Army had decided that a firing rate of 900 RPM was a disadvantage. It led to a dramatically increased total weight of ammunition for both men and air transport. The increased security of the automatic selection could be had with short bursts.

Therefore, in the M16A2's first fire option, each pull of the trigger fires one shot. The other position automatically fires a three-shot burst for each trigger-pull. The U.S. Army performed years of experiments to discover and verify that three-shot groups were optimum, originally in order to develop a flechette rifle.

Besides the selector system, the M16A2 incorporates an adjustable dual-aperture rear sight that corrects for both windage and elevation, a heavier barrel to increase accuracy, 1-in-7 rifling, and an effective muzzle compensator to prevent muzzle climb during operation.

The XM-177E2 was the forerunner of the M4 Carbine, which was developed in the early 1990s, adopted officially in 1994, and was used with great success in the Balkans, the 2000s War on Terrorism, and in Iraq.

Currently (2003) the U.S. Army has issued limited numbers of the newest variants, the M16A3 and M16A4, which incorporate a rail mounting system similar to the M4A1 Carbine.

The type is often argued to have various technical problems and there is a general preference for the M-4 Carbine (an M16 variant). However, since the M-4 is also seen as somewhat archaic, many authorities believe that the M16 will be replaced by an "Objective Individual Combat Weapon." Other innovations that might obsolete the series are caseless ammunition and laser weapons.