RTB Barreled 16" 5.56 Upper Receiver | A2 | 15" M-LOK - Black Anodized This Barreled 16 inch M-LOK upper receiver comes with our RTB 15 inch free float handguard and is built with only the best Mil-Spec components. The heart of this upper is comprised of a 4150 barrel.Barrel: LENGTH - 16" MATERIAL - 4150 CHROME MOLY VANADIUM 11-DEGREE TARGET CROWN - FURTHER IMPROVE ACCURACY PROFILE - M4 FINISH - QPQ CORROSION RESISTANT GAS SYSTEM LENGTH - CARBINE GAS BLOCK JOURNAL - .750" GAS BLOCK JOURNAL TWIST RATE - 1/7 TWIST MUZZLE - 1/2X28 THREADED WEIGHT - 28OZ Upper Receiver: Machined from a Mil-Spec 7075 T6 forging Hard Coat Anodized per Mil-A-8625F, Type III M4 Feed ramps Made in the U.S.A. Handguard: MATERIAL: HARD COAT ANODIZED ALUMINUM HANDGUARD, ALUMINUM BARREL NUT PRECISION BORE ACCEPTS M-LOK RAIL SECTIONS & ACCESSORIES 7075-T6 BARREL NUT RAIL LENGTH IS MEASURED ALONG THE TOP INNER DIAMETER: 1.36" SKU: RTBBU-1655615-BLK UPC: