Barrel: 20" 416R stainless steel barrel. Chambered in 5.56 NATO, with a 1:7 twist rate, M4 barrel extension, and a rifle-length gas system. Barrel is finished off with a PSA 15" Lightweight M-Lok free float rail, .750" low-profile gas block, and an A2-style flash hider. Upper: Forged 7075-T6 aluminum A3 AR upper is made to MIL-SPECS and hard coat anodized black for durability. These uppers are made for us right here in the USA by a mil-spec manufacturer. Bolt: Full-auto profile bolt carrier group. Milspec Carpenter No. 158A(R) steel bolt. Gas Key Hardened to USGI Specifications, Fastened with Grade 8 screws, and Staked per Mil-Spec.