Bore
The inside of a rifle barrel, the channel the bullet travels down. Bore diameter is measured between the lands, not the grooves.
A .308 bore measures .308 inch across the lands. The grooves are deeper (about .003 inch), so the same barrel measures roughly .311 across the grooves.
Different bullet weights and shapes can be shot from the same bore as long as the twist rate supports them. Bore condition (fouling, throat erosion, copper deposits) matters more than absolute diameter once you’re past a few hundred rounds.