The M4 Carbine is a shorter and lighter version of the M16A2 assault rifle, achieving 80% parts commonality with the M16A2. The M4 has select fire options including semi-automatic and three-round burst (like the M16A2), and the M4A1 has a full auto option in place of the three-round burst. As with many carbines, it is handy and more convenient to carry than a full-length rifle. Here an M4 is shown just after firing, with an ejected ammunition casing in mid-air. Photo credit: Suzanne M. Day, U.S. Air Force |