Barrel: 4150V Chrome moly steel, chambered in 5.56 NATO, with a 1:7 twist, M4 barrel extension, nitride treated, and a carbine-length gas system. Barrel is finished off with a .750" diameter low-profile gas block, PSA 15" Lightweight M-Lok free float rail, and A2 flash hider. Upper: Forged 7075-T6 A3 AR upper is hard coat anodized black for durability. Featuring M4 feedramp cuts, these upper receivers are made for us right here in the USA. Bolt Carrier Group: For AR15 and M16 rifles and carbines. Bolt is made of shot-peened, Mil-spec Carpenter 158(R) steel. Gas key is secured with grade 8 fasteners and staked. Lower Build Kit: Includes the PSA Classic Freedom Lower Build Kit