Barrel: The 16" 4150V Chrome Moly Vanadium steel Nitride barrel is chambered in 5.56 NATO, with a 1:7 twist, M4 barrel extension, and a Midlength gas system. The barrel is finished with a .750" diameter low-profile gas block, PSA 13.5" Hex Full Picatinny M-LOK Free Float Rail and an A2 flash hider. Upper: Forged 7075-T6 A3 AR upper is machined to MIL-SPECS and hard coat anodized. These Left-handed uppers are made for us right here in the USA by a mil-spec manufacturer. Bolt: Full-auto profile left-handed bolt carrier group. 9310 steel bolt, Shot Peened, Gas Key Hardened to USGI Specifications, Fastened with Grade 8 screws, and Staked Per Mil-Spec. 8620 steel M-16 profile carrier.