I’m not a lawyer etc etc. I think you know where I am going.
I could absolutely be wrong on this. So don’t savage me over it.
I think that what makes black powder weapons legal. Is it being considered an antique
If your black powder gun is a newly manufactured model such as a Remington Model 700 Muzzleloader, then it will be regulated by all applicable laws relating to the carrying and possession of a firearm because it is not a replica of a pre-1899 gun.
I would worry that an overzealous “somebody” would try to call it an AOW. Since it’s made with modern manufacturing processes.
I have no idea on the legality. From a self defense perspective it would be a two shot short barrel shotgun that transforms into a very short club after you fire it. Unless the criminals you are facing are very polite and standby while you reload.
I suspect the pattern from such a short barrel would open up pretty quickly? Might be an advantage at very short ranges but could be a significant liability at anything past close range.