Saw a video on youtube, the guy knows what he’s doing.
Takes a break action shotgun, takes a shotgun shell and cuts the plastic off. Knocks the spent primer out of it it, seats a new primer in it.
Inserts it in the gun. Muzzle Loads. Fires. Repeats.
Personally I would think you could do that without cutting the plastic off, in which case you’ve got the powder, shot, and wads all self contained as if you HAD reloaded the shotgun shell. Because you essentially have, even if its a fairly crummy reload, because a break action shotgun is somewhat forgiving on that note.
Still I think even better would be to take a break action .45-70 and do the same thing. Because it’s rifled, and it’ll accept just about any kind of .45 slug or less.
A revolver is also good for muzzleloading/caseless use, because In the old days the colt cavalry revolver was reloaded that way. They used crisco to seal the bullet in (so you only need one wad, not two).