These weapons are only capable of fully automatic fire, with a special side plate mounted inside the lower receiver and a selector that only has "safe" and "auto" positions. These weapons retain a 65% parts commonality with standard M16 rifles. Only the M196 tracer round was authorized for operational use, with the M199 dummy and M200 blank for training use. In an emergency, M193 ball ammunition was to be used. The heavier M855 ball and M856 tracer rounds were never to be used.