Prefit Barrel
Also: Shouldered Prefit
A pre-chambered barrel that headspaces by a shoulder or barrel nut, letting an owner swap barrels at home without a gunsmith and a lathe.
A prefit barrel arrives already chambered and threaded to a specific action, designed so the owner can install it without cutting any steel. It sets headspace either against a precisely machined shoulder that bottoms on the receiver, or against an adjustable barrel nut that the user clamps at the right depth using a gauge.
This system turns a job that once required gunsmithing and a lathe into an at-home swap with hand tools, which is why prefits are popular on actions like the Remington 700 pattern and modern custom designs. The owner can keep several barrels chambered for different cartridges and change them in minutes, and on many designs the recoil lug is captured at the same joint.