There are several pages of very similar single shot Target Pistols (mostly Belgian made) in the 1911 edition of the German ALFA catalog (think European version of Bannermans').
Indoor shooting was a thing towards the end of the 19th century. Even Sherlock Holmes did it.
1. From the plate at the back, the cylinder looks like it was designed for cartridges or converted from percussion to cartridges.
2. The brass ring in front of the cylinder is on what may have been a pull-pin, was part of the break-down method for cleaning.
3. The trigger arrangement reminds me of the ring-cocking Pepperboxes. That plate below the trigger probably advanced the cylinder when pushed down and returned.
My best guess is that they were stolen and later disposed of to get rid of the evidence, probably stolen in the burglary of a hardware store or something like that. Just a guess though. But I can almost assure you that they had some involvement in a crime or crimes.
You might want to check with your local county historian or historical society to see if anyone knows of any crimes from long ago that might fit with what you found.
... and since they're not exactly the most appealing designs for criminal enterprises, dumped in a sack in the nearest creek while the thieves exited stage left.
I agree fully, except the cylinder has no bolt stop slots and there must have been a provision of some sort indexing/timing slots on the rear plate of the cylinder. How that was accomplished is not apparent.[/QUOTE]
2. The brass ring in front of the cylinder is on what may have been a pull-pin, was part of the break-down method for cleaning.
I agree, but since the brass "barrel lug" encompasses most of the top of the adjacent part of the frame, just pulling that ringed pin will not allow the barrel assembly to be removed from the gun, unless it is so loosey-goosey to allow it. I think the "wedge" looking piece at the rear of the cylinder will have to be removed first, but that might secure the cylinder pin/arbor to the frame.
3. The trigger arrangement reminds me of the ring-cocking Pepperboxes. That plate below the trigger probably advanced the cylinder when pushed down and returned.
You may be very correct about that, but that would be a double-action if it also cocked the hammer. If not, the trigger would have to pulled again to release the hammer sear to fire the hammer. IMO, way too complicated for this gun.
Good luck with your inquiries... it's killing me because I swear I've seen some of those guns before somewhere... I suspect they all date post Civil War though.
They could be the work (mostly) of a home smith... and a mix of both home made and professional guns says possibly criminal origins. Especially found as they were in a large group. The workmanship on some of the guns kind of reminds me of guns from China in the 1920s, where there was small factories turning out guns that weren't quite professional.
It looks like some of them are Jongen target or salon pistols. Collette patent. Some were 20 shot gravity fed and used a bullet somewhat like the volcanic. Short, pointed, with powder and primer at the base. No shell casing. For more info look at forgottenweapons.com and horstheld.com Made in Liege Belgium patented in 1855 and made until at least 1870.