DPMS M-Lok 5.56x45mm NATO 16 inch Upper Receiver One Size. 56 NATO with a 1: twist M4 barrel extension and a mid-length gas system. The A2 profile barrel is finished with Phosphate. Barrel is finished off with an .750in diameter low-profile gas block DPMS 13.5in Lightweight M-Lok Free Float Rail and an A2 flash hider. Upper: Forged 7075-T6 A3 AR upper is hard coat anodized black for durability. Featuring M4 feedramp cuts these upper upper receivers are made for us right here in the USA. Bolt Carrier Group: For AR15 and M16 rifles and carbines. Bolt is made of shot-peened Mil-spec Carpenter 158 steel. Gas key is secured with grade 8 fasteners and staked. Includes Charging Handle. Specifications for DPMS M-Lok 5.56x45mm NATO 16 inch Upper Receiver: Manufacturer: DPMS Caliber: 5.56x45mm NATO Barrel Length: 16 in Gas System Length: Carbine Length Barrel Twist Rate: 1-7 Finish: Hardcoat Anodized Fabric/Material: 7075 T6 Aluminum Handguard Length: 13.5 in Barrel Material: Chrome Moly Vanadium Mount Type: M-LOK Package Contents: DPMS M-Lok 5.56x45mm NATO 16 inch Upper Receiver DPMS DP51655120177: M-Lok 5.56x45mm NATO 16 inch Upper Receiver One Size