The Live Free Armory Challenger 9mm PCC operates on a straight blowback system and does not require a gas block and gas tube as traditionally found in other AR15s. The direct blowback system uses the kinetic energy generated from the discharge of the cartridge, to push the bolt back and cycle the action. The Challenger is compatible with standard frame GLOCK G17/G19 pattern magazines. The receivers are machined from custom 6061-T6 billet aluminum. The LFA Challenger utilizes a 16" barrel. These barrels are manufactured with the same quality and attention to detail as our AR15/AR308 you know and love. The free float handguard measures in at 15" M-lok compatible, and free float handguard.