H&R and I believe Rossi have single shot rifles with interchangible barrels.
AFAIK, no.
TC is one
Yes they should be.
Not every single mauser bolt is interchangable, but most bolts for a single model will be. For example, most bolts from the millions of WWII era kar-98k's are interchangable but will not be interchangable will a modern mauser hunting rifle or a modern rifle based off of the mauser action.
No
Among other BPS shotguns, yes.
model 158 12 gauge shotgun
colt
No, the gun is either chambered for one gauge or the other.
Rossi is coming close with a single shot rifle ( the wizard) with interchangable barrels. They boast 21 different combos and include shotguns. As far as a gun that can shoot everything from a 17 HMR to a 50 caliber bullet the answer is no.
Heavy Barrel
Rifle Muskats Sub Mrines Rifle Barrels Cannons