Fire bullets from a shotgun?

Context: I don't have a FAC. Getting the stupid questions out of the way first.

While looking to see what kind of entry-level plinking rifles were available, I discovered a weird thing I hadn't seen before: .22 and 9mm bolt-action shotguns. Plentiful and cheap by the look of it.

Could I plan to get one of these and use it with the right-sized bullet on an indoor range? Why not? (I assume the answer is likely 'no')

First thing, I guess using bullets immediately changes the gun's licence category... Is this just a matter of having the FAC instead of the SGC, or does this count as some kind of "misuse" or illegal "modification"?

Second thing, even if the calibre is right, would the mechanism be compatible? Would there be safety issues with e.g. overpressure vs. the intended use?

Third (bonus): what *is* the intended use for such guns? I think of shotgun shells as big objects that sling a lot of lead. .22 ...not so much. How would you use one in a SGC-compatible way anyway?

Or are they just cheap because they're essentially obsolete and there's no modern legal use case?