CALIBER: 5.56 NATO BARREL LENGTH: 16 TWIST RATE: 1:8 PROFILE/CONTOUR: M4 MATERIAL: 4150 CHROME MOLY VANADIUM FINISH: PARKERIZED GAS SYS: CARBINE DIAMETER AT GAS PORT: .750 MUZZLE THREAD: ½-28 TREATMENT: NON-RF85 ADDITIONAL NOTES: Barrel is compatible with .223 Ammunition.