Barrel: The Nitride treated 4150V chrome moly steel is chambered in 300AA Blackout, with a M4 barrel extension, and pistol-length gas system. This heavy profile barrel is finished off with a PSA 12" Lightweight Slant End M-Lok free-float rail, .750" low-profile gas block, and PSA Fluted Flash Can. Upper: Forged 7075-T6 A3 AR upper is hard coat anodized. These uppers are made for us right here in the USA! Bolt: Full-auto profile bolt carrier group. Shot-peened, mil-spec Carpenter No. 158A(R) steel bolt. Gas Key Hardened to USGI Specifications, Fastened with Grade 8 screws, and Staked Per Mil-Spec. 8620 steel M-16 profile carrier. Lower: These forged lowers are quality made using 7075-T6 aluminum and are marked "MULTI" for caliber. The lower finish is hard coat anodized. The 7075-T6 buffer tube is hard coat anodized and is fitted with an SB Tactical SBA3 Adjustable Pistol Brace, Magpul Grip, and Enhanced Polished Trigger (EPT).