Barrel: Nitride finished 4150V chrome moly vanadium 16" barrel. Chambered in 5.56 NATO, with a 1:7 twist, M4 barrel extension, and a carbine-length gas system. Barrel is finished off with Magpul MOE mid-length handguards, F-Marked gas sight base, and A2 flash hider.Upper: Forged 7075-T6 A3 AR upper is made to MIL-SPECS and hard coat anodized 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, Shot Peened, High pressure tested, Mag particle inspected, Gas Key Hardened to USGI Specifications, Fastened with Grade 8 screws, and Staked Per Mil-Spec. Includes: Magpul MBUS Rear Sight - Black. The US made MBUS (MagpulA(R) Back-Up Sight) is a low-cost, color injection molded, folding back-up sight. The dual aperture MBUS Rear Sight is adjustable for windage and fits most 1913 Picatinny rail equipped weapons, but is specifically tailored to the AR15/M16 platform. Spring-loaded flip up action is easily activated from either side or by pressing the top. Impact resistant polymer construction provides light weight and resists operational abuse.