Heckler & Koch USA (HK USA) MR556 A1 Complete Upper Receiver 16.5" Gas-Piston 5.56 NATO
This HK MR556 A1 complete upper receiver assembly is a 5.56mm NATO, short-stroke gas-piston design built around HK’s piston/operating rod system. It is configured with a free-float handguard and a continuous Picatinny top rail for optics and accessories.
Factory configuration features a 16.5" cold hammer forged, unlined barrel with 1:7" twist and 6 lands & grooves rifling. A flash hider is installed, and the bolt carrier group is present.