Muzzle velocity 975 m/s (3,200 ft/s ), 930 m/s (3,050 ft/s) (see Variants ) Effective range 550 m (600 yd ) Feed system 20- or 30-round detachable box magazine (see Design ) A U.S. soldier on exercises with an M16A1 and M40 Field Protective Mask : note the forward assist on the receiver and