5.56mm Semiautomatic Rifle

General dissatisfaction with the M14 and numerous studies led the Army to the development of a light weight weapon capable of firing a burst of small caliber bullets with a controlled dispersion pattern. Although opposed by the Ordnance Corp, the Armalite AR-15 was adopted by the Secretary of Defense as the 5.56mm M16 rifle. The M16 was selectable for full and automatic fire. The M16 was to have had the same effective range as the M14 rifle it replaced, but it was most effective at a range of 215 yards (200m) or less. The M16 used a 5.56mm (.223 cal.) cartridge in 20- or 30-round magazines. There were a number of problems encountered during initial fielding, but better training, preventive maintenance, and several design changes, resulted in the weapon that has become the standard issue rifle of the US Army , with some 3,690,000 having been manufactured.

The M16A2 semiautomatic rifle is the standard by which all military rifles of the future will be judged. This variant of the M16 fires a three-round burst in semiautomatic operation. The system incorporates an adjustable rear sight which corrects for both wind and elevation, a heavier barrel with 1-in-7 rifling, and a muzzle compensator to prevent muzzle climb during semiautomatic operation. The M16A2 is capable of firing all NATO standard 5.56mm ammunition and can fire 40mm grenades when equipped with the M203 Grenade Launcher.

The M4/M4A1 5.56mm Carbine is a lightweight, gas operated, air cooled, magazine fed, selective rate, shoulder fired weapon with a collapsible stock. A shortened variant of the M16A2 rifle, the M4 provides the individual soldier operating in close quarters the capability to engage targets at extended range with accurate, lethal fire. The M4 Carbine achieves over 80% commonality with the M16A2 Rifle and will replace all M3 .45 caliber submachine guns and selected M9 pistols and M16 rifle series.

The M16A2 5.56mm rifle is a lightweight, air-cooled, gas-operated, magazine-fed, shoulder- or hip-fired weapon designed for either automatic fire (3-round bursts) or semiautomatic fire (single shot) through the use of a selector lever. The weapon has a fully adjustable rear sight. The bottom of the trigger guard opens to provide access to the trigger while wearing winter mittens. The upper receiver/barrel assembly has a fully adjustable rear sight and a compensator which helps keep the muzzle down during firing. The steel bolt group and barrel extension are designed with locking lugs which lock the bolt group to the barrel extension allowing the rifle to have a lightweight aluminum receiver.

The M16A2 rifle is a product improvement of the M16A1 rifle. The improvements are:

· a heavier, stiffer barrel than the barrel of the M16A1;

· a redesigned handguard, using two identical halves, with a round contour which is sturdier and provides a better grip when holding the rifle;

· a new buttstock and pistol grip made of a tougher injection moldable plastic that provides much greater resistance to breakage;

· an improved rear sight which can be easily adjusted for windage and range;

· a modified upper receiver design to deflect ejected cartridges, and preclude the possibility of the ejected cartridges hitting the face of a left-handed firer;

· a burst control device, that limits the number of rounds fired in the automatic mode to three per trigger pull, which increases accuracy while reducing ammunition expenditure;

· a muzzle compensator, designed to reduce position disclosure and improve controllability and accuracy in both burst and rapid semi-automatic fire;

· a heavier barrel with a 1 in 7 twist to fire NATO standard SS 109 type (M855) ammunition which is also fired from the M249 Squad Automatic Weapon (SAW). This further increases the effective range and penetration of the rifle cartridge. The M16A2 will also shoot the older M193 ammunition designed for a 1 in 12 twist.