This is a "made-up" trapdoor carbine; it started as a "Bannerman Fake", purchased by the late gunsmith Roger Denton, who, knowing it was not a genuine collectable, cut it down into a short-handled "camp shotgun" for .410 shells!
I was given the piece and restored it into a useable carbine, using both a new stock and buttplate, and genuine original replacement parts obtained from Dixie Gun Works back in the 1970's.