A direct descendant of the world-famous HK416, the MR556A1 is the commercial carbine from the same DNA. It offers the battlefield-proven reliability, durability and precision you would expect from a rifle that bears the name Heckler & Koch. Like the HK416, the MR556A1 uses a proprietary HK short-stroke gas piston in place of the direct-gas-impingement system found on lesser AR15-style rifles that propels exhaust gas into the upper receiver to operate the action. In the "closed" HK piston system, exhaust gasses never enter the receiver, which means the HK runs cooler, cleaner and more reliably. This model features a Juggernaut Tactical magazine lock kit and includes one 10-round magazine.