A groove in a rifle stock or fore-end where the barrel fits in the assembled position.
Letter: B
BARREL DIAMETER
The outside dimension of a barrel at any given point.
BARREL EROSION
The wearing or physical deterioration of the bore or chamber of a firearm caused by hot propellant gases or projectile passage.
BARREL EXTENSION
A metal projection which extends rearward from the breech end of a barrel into which the breech locks while the firearm is in battery or firing position.