Barrels are engraved CMMG MPC 5.56 NATO 1:9. Each upper is head spaced and test fired before shipping. The upper is built off of our standard forged A3 receiver with M4 feed ramps. The barrel is our 4140 steel, Bull Barrel profile, 5.56mm chamber and bore and 1:9 twist ratio. The upper includes a low profile gas block and smooth free float tube.