The M27 Infantry Automatic Rifle (IAR) is a lightweight, magazine-fed 5.56mm weapon used by the United States Marine Corps. It is intended to enhance an automatic rifleman's maneuverability, and it is based on the Heckler & Koch HK416.
The M27 is based on the Heckler & Koch HK416. 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. Alternate calibers other than 5.56 mm are being considered for the M27.