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.
Among other BPS shotguns, yes.
model 158 12 gauge shotgun
No
colt
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.
No, the gun is either chambered for one gauge or the other.
Heavy Barrel
The 916A does not have an interchangeable barrel- the owners manual indicates that barrels are not removeable, but are permanently installed at the factory. The link below will take you to the owner's manual for the S&W Eastfield 916A.