AR chassis is completely coated inside and out with NiB-X (Nickel Boron) and topped with ceramic color finish. Carbine-length gas system. NiB-X coated M4 flat-top upper and lower receivers. NiB-X coated bolt carrier group and charging handle. Case hardened, shot peened and magnetic particle inspected Carpenter 158 bolt with Mil-Spec gas rings. NiB-X coated fire control parts. NiB-X coated 16 inch 4150 Chrome Molybdenum Vanadium barrel with Nitromet coated bore. 1:7 inch twist. Gas block is shipped loose for attachment of any hand rail. Just add furniture, hand rail and flash hider to complete your custom rifle. Made in the USA.