Ballistic Advantage Classic Series Barrel 5.56x45 10.3 inch Government Carbine 1-7 Twist Black. 56 chambered 16 inch M4 Carbine Length Classic Series Barrel is machined from 4150 Chrome Moly Vanadium steel with a chrome lined bore and chamber with a manganese phosphate finish and phosphate coated M4 feed ramp extension. Specifications for Ballistic Advantage Classic Series 5.56x45mm Barrel: Manufacturer: Ballistic Advantage Color: Black Finish: Phosphate Fabric/Material: 4150 CMV Caliber: 5.56x45mm NATO Gas System Length: Carbine Length Gas Block Journal Size-Diameter: .750 in Threads per Inch: 1/2x28 Barrel Twist Rate: 1-7 Country of Origin: USA Package Contents: Ballistic Advantage 556014MC Classic Series 5.56x45mm Barrel What firearm models does the manufacturer say Ballistic Advantage Classic Series 5.56x45mm Barrel is compatible with? The manufacturer says that Ballistic Advantage Classic Series 5.56x45mm Barrel is compatible with AR-15Ballistic Advantage BABL557103MC: Classic Series Barrel 5.56x45 10.3 inch Government Carbine 1-7 Twist Black