The barrel is a metal tube through which the projectile travels.
- The interior of the barrel. The bore may be smooth or rifled.
- The rear end of the barrel, closed by a part called the breech plug. There are three types of breech plugs:
- The open end of the barrel, where the projectile leaves the gun. In a muzzleloading firearm, the powder charge and projectile are loaded into the muzzle.