The M16 is the standard U.S. Army issue rifle. It is semi-automatic, and fires 5.56 x 45mm ammunition. The weapon is fed by a 30 round magazine that mounts just forward of the trigger.
Background
In 1963, the M16 entered United States Military service and was deployed for jungle warfare operations during the Vietnam War. In 1969, the M16A1 replaced the M14 rifle to become the U.S. military's standardservice rifle. The M16A1 improvements include a bolt-assist, chromed plated bore and a new 30-round magazine. In 1983, the USMC adopted the M16A2 rifle and the U.S. Army adopted it in 1986. The M16A2 fires the improved 5.56×45mm NATO (M855/SS109) cartridge and has a new adjustable rear sight, case deflector, heavy barrel, improved handguard, pistol grip and buttstock, as well as a semi-auto and three-round burst only fire selector.