The M16 is a select-fire assault rifle which has become synonymous with American forces in the Vietnam War. It is derived from the earlier Colt Armalite AR-15 designed by Eugene Stoner. It began to be issued in the early 1960s but would not begin true mass production until well into the mid-1960s due to severe unreliability problems. The M16 is typically issued with 20-round magazines of .223 Remington, an intermediate cartridge.