The art M5E1 platform starts here, with the M5E1 Upper Receiver. The M5E1 upper receiver is a one-piece design combining the handguard mounting platform with the upper itself. Through superior engineering, Aero has condensed the parts needed to mount a free-floated handguard to a mere 8 screws. Since the handguard mounting surface and upper are of the same forging, not only is it a stronger system. Included is a M5E1 Upper Receiver, Port Door, Forward Assist installed & Barrel Nut.