The BCA AR-9 Barrel is a 5" made out of 4150 chrome moly vanadium steel with a parkerized finish, a 1:10 twist rate. The barrel is chambered in 9MM with a single feed ramp machined in the barrel extension and operates with a blowback gas system. All Finished Barrels go through a 100% Inspection Process. Inspections Equipment includes CMMs and Air Gauges for the Bores. 5" 4150 Black Nitride Barrel Slim Contour Barrel Profile 1:10 Twist 9MM Caliber