The M16A2 entered service in the 1980s and fired the NATO standard Belgian-designed M855/M856 cartridge.[2] The M16A2 is a select fire rifle capable of semi-automatic or three-round bursts and incorporating design elements desired by the Marine Corps.[2] These features included an adjustable rear-sight for windage and elevation, a 5/8 inch longer buttstock, heavier barrel, case deflector for left-handed shooters, and rounded handguards.[2] Mode of fire is determined by using a selector switch on the side of the weapon. The M16A3 was essentially an M16A2 with an M16A1 fire control group; this had only limited procurement by the USN. (FULL AUTO)
The M16A4 became standard issue for the United States Marine Corps during Operation Iraqi Freedom, increasingly replacing the earlier M16A2. In the United States Army, a combination of the M16A4 and M4 Carbine continues to replace existing M16A2 Rifles. The A4 incorporates a flattop receiver unit developed for the M4 Carbine, a handguard with four Picatinny rails for mounting optical sights, lasers, night vision devices, forward handgrips, removable carry handle and flashlights.