Huh. Has an entry thimble, so presumably a ramrod hole drilled in it, but it would be difficult to use that ramrod.....
I'm going to guess that that is two different guns there, a Twigg minus its barrel, and a barrel minus its lock and stock. The blunderbuss must have had a standing breech too, for it to fit in The Twigg stock. At the back of my mind I'm remembering something, possibly from Peterson's Great Guns, about late Liege-made blunderbusses with very exaggerated flares - it is that and the (presumed) standing breech that makes me think it might have been on an actual gun at some point, and not just a prop barrel.