RTB Barreled 10.5" 5.56 Upper Receiver - Black | A2 | 9" M-LOK This Barreled 10.5 inch M-LOK upper receiver comes with our RTB 9 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 Specifications Caliber 5.56 Length 10.5" Material 4150 Chrome Moly Vanadium Profile Government Finish QPQ Corrosion Resistant Gas System Length Carbine Gas Block Journal .750" Dimpled? No Twist Rate 1:7 Muzzle Thread 1/2x28 TPI Weight 18.4oz Barrel Extension M4 Feed Ramps Target Crown 11 Degree Upper Receiver: Machined from a Mil-Spec 7075 T6 forging M4 Feed ramps Made in the U.S.A. Handguard: MATERIAL: BLACK 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" ***Please allow an additional 2-3 business days of lead time as these uppers are made to order.*** SKU: RTBBU-1055569A2-BLK UPC: