Steel
You will have to replace the barrel
Not a generally used term- it would be the portion of a gun that holds the barrel. Not present on all guns.
Any autococker threaded barrel.
Oxidation of the steel of a gun barrel.
No
See the link below
The BSS
Did marlin make a goose gun with a thirty nine inch barrel
The first gun with a rifled barrel (a rifle is any gun with grooves cut into the barrel to give the projectile spin) used by American forces was the Kentucky rifle, used in the revolutionary war.
I do not personally, but yes, there is a single shot rifle that can have the rifle barrel replaced with a shotgun barrel.
Basically they are the same. But a long Barrel and a long shoulder stock make a gun a Rifle.
It is in different places depending on the gun, but typically, it will be somewhere on the barrel or on the lower frame of the gun.