Diamondback Barrels AR-15 Nitride Barrel 8.5in .300BLK 1-8 Twist Rate 5/8 X 24 TPI 300P8.5H50B8. This barrel is machined from 4150 Chrome Moly Vanadium Steel and features 5R rifling to ensure consistent accuracy and has a 1:8 twist rate. The pistol...