DPMS M-Lok .300 AAC Blackout 7.5 inch Upper Receiver One Size. 5in Chambered in 300AAC Blackout with a 1:8 twist rate M4 barrel extension and a pistol length gas system. This phosphate barrel is finished off with a DPMS Lightweight M-Lok free-float rail .750in diameter low profile gas block and an A2 flash hider. Upper: Forged 7075-T6 A3 AR upper is made to MIL-SPECS and hard coat anodized black for durability. These uppers are made for us right here in the USA by a mil-spec manufacturer. Bolt: Bolt is made of Mil-spec shot-peened Carpenter 158 steel. Gas key is secured with grade 8 fasteners and staked per mil-spec. Bolt carrier is parkerized outside and chrome lined inside. Specifications for DPMS M-Lok .300 AAC Blackout 7.5 inch Upper Receiver: Manufacturer: DPMS Caliber: .300 AAC Blackout Barrel Length: 7.5 in Gas System Length: Pistol Length Barrel Twist Rate: 1-8 Threads per Inch: 5/8x24 Finish: Phosphate Gas Block Journal Size-Diameter: .750 in Handguard Length: 7 in Bolt Carrier Group Included: MIL-SPEC Charging Handle Included: MIL-SPEC Length: 17 in Package Contents: DPMS M-Lok .300 AAC Blackout 7.5 inch Upper Receiver DPMS DP51655111877: M-Lok .300 AAC Blackout 7.5 inch Upper Receiver One Size