Barrel: This Chrome Moly vanadium 4150V barrel is chambered in .300 AAC Blackout with a M4 barrel extension, and a pistol-length gas system. It is nitride treated for accuracy and durability and is finished off with a .750" diameter gas block, a PSA 15" Lightweight M-Lok free float rail, and an A2 Flash Hider. Upper: The forged 7075-T6 A3 AR upper is machined to MIL-SPECS and hard coat anodized. These uppers are made for us right here in the USA by a mil-spec manufacturer. Build Kit: Includes Classic M4-Style Stock, A2 Pistol grip, Classic Lower Parts Kit and Mil-Spec diameter 6-position buffer tube assembly. Everything you need to finish your stripped lower! Sight Set: Magpul MBUS Sight Set, Black