One imagines that that's the domain of some pretty hardcore hobbyists. Given the utterly different engineering requirements, if you just want a blaster that looks like an old-fashioned slugthrower, it is probably easier and cheaper to have it scratch-built by a professional blastersmith¹ than it is to convert an already existing slugthrower into a blaster.

But that wouldn't be as much fun. :)

-Merc
Keep Rat

¹If this isn't a word, it should be.