Quote:
The trigger/hammer group is basically similar to one, found in M1 Garand rifle, and, actually, traces its roots back to the early 1900s, when the great John M. Browning developed his famous Auto-5 semiautomatic shotgun. This basically consists of a hammer, a trigger, a disconnector, a full auto sear and some springs. The fire selector / safety switch is located at the left side of the receiver, above the pistol grip, and is easily operated by the right hand thumb. This switch has 3 positions: "safe", "semi" (single shots), and "auto" (full automatic on M16A1 and A3) or "burst" (3 rounds bursts, on M16A2 and A4). In the latter case (on the M16A2 and A4 rifles), the trigger unit also includes the ratchet device to count the shots fired.