Currently in use by US troops, the M4 is a shorter and lighter version of the M16A2 assault rifle, achieving 80% parts commonality with the M16A2. The M4 has selective fire options including semi-automatic and three-round burst (like the M16A2). Fires 5.56 x 45 mm NATO cartidges at a rate of 700950 round/min fed from a 30-round detachable box