The M27 Infantry Automatic Rifle is a Light Machine Gun produced by Heckler and Koch . It was designed as a support weapon variant of the HK 416 Assault Rifle, and is compatible with standard 5.56mm STANAG magazines. The M27 is based on the Heckler & Koch HK416, which in turn derives from the M4 carbine and Heckler & Koch G36. It features a gas-operated short-stroke piston action with a rotating bolt. The free-floating barrel is surrounded by MIL-STD-1913 Picatinny rails for use with accessories and optics. The simpler gas-piston rifle system reduces the amount of time it takes to resolve malfunctions on the IAR compared with the M249. The M27 is so similar to the standard M16A4 that its bolt carrier can fit into one and chamber a round. Conversely, an M16 bolt carrier cannot fit into an M27. Alternate calibers other than 5.56 mm are being considered for the M27. It is currently used by the Alliance Joint Marine Corps.