I've spent some of what is left of my life looking at this gun, and I've concluded that is is, in fact, a complete frawk, a portmanteau word meaning a decoration piece that looks something like an old-style firearm that is used to jolly-up the interior of trendy pub somewhere. The crudeness of the manufacture tells me that it may never have been intended to be fired at all. The cast-in sling 'swivel' lug on the trigger guard is nothing like anything thing I've ever seen before, but the clincher, for me, is that the barrel and lock appear to be cast in one piece (????).
However, there is the proviso that I've not seen everything there is, as I'm shown every time I log onto this site.
PLEASE don't try and fire it.