This is a prefit barrel that utilizes a barrel nut system to tighten the barrel onto the action. The benefit of this style of barrel is that it's easily fit up by anyone at home with a proper wrench and headspace gauges. 5 minutes is all you need to swap from one caliber to another, so you can easily run one action, one chassis and one scope while switching just the barrel from .308 to 6.5 Creedmoor for example. Mfg: International Barrels