bolt
breech
The bolt.
Bolt
bolt
I would think the bolt sliding forward in the receiver would close the aperture.
bolt
The bolt.
To make the rifle easier to handle in tight spaces, or to remove a section of the barrel near the muzzle that has been damaged.
telescopic aperture battle
I do not personally, but yes, there is a single shot rifle that can have the rifle barrel replaced with a shotgun barrel.
That term refers to the outline shape of the outside of a rifle barrel.
Impossible to answer without knowing the model of the rifle.