Manufactured in the United States using premium components, the BRN-15 upper receiver groups serve as an excellent foundation for your next build. To complete the assembly, select your preferred Bolt carrier group and charging handle. The BRN-15 upper receiver groups are equipped with a 5.56x45mm chambered barrel featuring a nitride finish, available in various popular lengths. Each barrel includes a gas block dimple, ensuring secure engagement with the rear gas block screw. All barrels undergo stress relief processes. The distinctive M-LOK handguard extends beyond the gas block, maximizing usable space. Anti-rotation tabs at the rear of the handguard engage with the upper receiver maintaining alignment with the receiver's picatinny rail. Dual large screws clamp through the properly torqued barrel nut, preventing forward slippage of the handguard. Additionally, large vents positioned towards the rear facilitate rapid cooling of both the barrel and handguard. 4150 chrome moly vanadium (CMV) barrel 5.56x45mm Caliber 1:7 rifling twist rate Thread specification - 1/2-28 muzzle A2 flash suppressor 7075-T6 forged upper receivers Anodized upper receiver with hardcoat finish M4 feedramps in upper receiver and barrel extension Barrels are designated as 5.56x45mm, 1:7 twist, 4150CMV SR Manufactured entirely in the United States