Expect nothing less than professional grade weaponry from BCM. This Bravo Company Manufacturing Barreled Upper Receiver is built around a hand lapped, button rifled, MIL-SPEC SS410 stainless steel barrel. Harder and more corrosion resistant than conventional 416 stainless steel, the SS410 barrel offers the best balance of weight and accuracy.The BCM MCMR Handguard eliminates external load on the barrel, reducing deflection for more accurate shooting. M-LOK mounting slots and a continuous Picatinny rail provide all the space you need for your favorite accessories.Features: 18" SS410 stainless steel barrel Chambered in 5.56 NATO with 1:8 twist rate 1/2x28 A2 Flash Hider High pressure tested and magnetic particle inspected M4 feed ramps T-Marked Picatinny rail 15" BCM MCMR M-LOK Free Float Handguard