Due to a process called Single Point Cut Rifling, these replacement barrels have an exact twist and a more uniform bore and groove. These barrels are pre-lapped before rifling and finish-lapped after rifling. This black .308 Win barrel is 20" in length with a M18x1.5 thread and fits Accuracy International A/AX short action rifles. Accuracy International .308 Win M18x1.5 20" AT/AX Barrel 1420061BL