Switch Barrel
A rifle built so barrels swap quickly to change caliber or replace a worn tube while holding zero and correct headspace.
A switch-barrel rifle is designed so the barrel comes off and goes back on quickly, usually with simple hand tools, letting one action serve several chamberings. The system depends on barrels machined to a repeatable interface, often a prefit barrel tightened by a barrel nut or an indexing clamp, so each tube returns to the same position every time. A shooter can run a .223 for practice and a magnum for distance on the same receiver and chassis.
The two things that must survive a swap are headspace and zero. Well-built switch-barrel systems set headspace into each barrel during fitting so it stays correct on reinstall, and many mount the optic to the barrel or to a rail that indexes consistently, so point of impact returns close to where it left. This makes the concept popular with traveling competitors and handloaders who want to stretch one quality action across many calibers.