Barrel: Nitride finished 4150V chrome moly vanadium 16" barrel, Chambered in 5.56 NATO, with a 1:7 twist rate, M4 barrel extension, and a carbine length gas system. The barrel is finished off with B5 Systems MLOK carbine length handguard, a .750 F-Marked front sight base, and an A2 flash hider. B5 Systems MLOK Carbine Handguard: Slim profile for improved ergonomics Durable composite construction Integral heat shield 6 side M-LOKA(R) attachment Built-in hand stop Compatible with both round and triangle handguards Made In The USA 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, gas key hardened to USGI Specifications, fastened with grade 8 screws, and staked per Mil-Spec. 8620 steel M-16 profile carrier.Lower Build Kit: Includes B5 Systems Bravo stock, B5 P-Grip, Classic Lower Parts Kit, and Mil-Spec diameter 6-position buffer tube assembly. Everything you need to finish your stripped lower.