US Patent 7316091 Firearm bolt carrier with mechanical/gas key

A firearm includes a barrel having an end coupled to a receiver. A reciprocating bolt carrier is carried by the receiver and movable between a locked position and an unlocked position. The bolt carrier includes a buttress formed in a top surface thereof. A key includes a base having a rearward end and is coupled to the bolt carrier with the rearward end abutting the buttress.