Franklin Armory Militia Model 308 Winchester 20 inch Rifle Length Barrel Black. 5 inch Barrel Midlength Gas System or 20 inch Barrel Rfile Length Gas System. 7.62x51 NATO/.308 WIN. 4140 Chromoly Steel. Salt Bath Nitride Chamber Bore and Finish. 1/10 inch Twist rate. Threaded. Specifications for Franklin Armory Militia Model 7.62x51/308 Winchester Barrel: Manufacturer: Franklin Armory Color: Black Finish: Salt Bath Nitride Caliber: 7.62x51mm NATO .308 Winchester Barrel Length: 20 in Gas System Length: Rifle Length Barrel Twist Rate: 1-10 Additional Features: 5/8in-24 Thread .750in Gas Block Condition: New Package Contents: Franklin Armory Militia Model 7.62x51/308 Winchester Barrel Franklin Armory 5464: Militia Model 308 Winchester 20 inch Rifle Length Barrel Black