DPMS Quad-Rail 5.56x45mm NATO 16 inch Upper Receiver One Size. Exclusive Panther designed handguard with markings is only avilable on these new line of upper receivers. Barrel: 4150V Chrome Moly Vanadium Steel. Chambered in 5.56 NATO with a 1/7 twist M4 barrel extension and a Mid-length gas system. This A2 style profile barrel is nitride treated for accuracy and durability. Barrel is finished off with a low profile gas block a custom 9in quad rail handguard 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. Specifications for DPMS Quad-Rail 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 Handguard Length: 13 in Barrel Material: Chrome Moly Vanadium Bolt Carrier Group Included: MIL-SPEC Charging Handle Included: MIL-SPEC Package Contents: DPMS Quad-Rail 5.56x45mm NATO 16 inch Upper Receiver DPMS DP51655131214: Quad-Rail 5.56x45mm NATO 16 inch Upper Receiver One Size