HM Defense GuardianF5 5.56mm NATO / 223 Remington 16in Black Hardcoat Anodized Semi Automatic Modern Sporting Rifle - 30+1 Rounds Barrel: All HM Defense barrels are match grade, tripled honed and button rifled for superior accuracy. Chambered in 5.56 NATO / 223 Remington, the GuardianF5 4150 Chromoly barrel is 16in in length, features a 1: 7in twist ratio and a mid length gas system barrel. Black Nitride Finish. Rail: The custom HM Defense 10-3/8in, free float 1913 Picatinny rail is compatible with Magpul M-LOK mounting system. Lower Receiver: The GuardianF5 features a Mil-Spec Forged 7075-T6 Lower Receiver with Type III Class II Hard-Coat Black Anodized Finish. Upper Receiver: The GuardianF5 features a Mil-Spec Forged 7075-T6 M4 Upper Receiver with Type III Class II Hard-Coat Black Anodized Finish, M4 Feed Ramps, and a 1913 Picatinny rail flat top. Components: HM Defense rifles include an M16 bolt carrier group with patented HMB bolt and Mil-Spec components, including the trigger & fire control group, charging handle and buffer tube/spring. Custom Trigger Guard, CNC Machined Muzzle Brake, Steel Gas Block. End Plate: HM Defense rifles feature a custom Quick Disconnect (QD) end plate, Furniture: Rifle features a black Mil-Spec HM CQB stock and standard grip. Magazine: 30-Round Magazine included.