Barrel: 4150V chrome-moly steel chambered in 300 Blackout, with a M4 barrel extension, pistol-length gas system, and nitride treated for accuracy and durability. The heavy profile barrel is finished off with a PSA 6" Lightweight Hex Full Picatinny M-Lok Free Float Rail, .750" low-profile gas block, and A2 Flash Hider. 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 and the carrier 8620 steel. Lower: These forged lowers are quality made using 7075-T6 aluminum and are marked "MULTI" for caliber. The 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 MOE Grip and Polymer Trigger Guard, and Enhanced Polished Trigger (EPT).