Are there grooves filed into the muzzle that almost look like rifling? My first thought is that it's one of the many Belgian made screw barrel derringers made and exported in the 1800s.
There appears to be a lug on the barrel so I am guessing it is a screw barrel piece. It would have originally had a wrench that fit over the barrel at the lug allowing the barrel to be removed (another common style had a wrench that fit into a squared off or grooved muzzle to do the same thing). Guns of this type had a small powder chamber that you filled and then placed a ball on top and reseated the barrel. The slightly oversize ball made for a very efficient little pistol that got the most out of the small powder charge.
There were also cheaper but similar looking guns that loaded from the muzzle. They will not have a lug or the shaped muzzle of a screw barrel piece. Belgium was probably the largest producer of cheap pocket guns of these types but it's not uncommon to find better quality versions from British makers. Does yours have any proof marks or a retailers name? Guns of this type were rarely marked with the makers info, they were intended to be sold through retailers and catalog sales. Proof marks are usually the only way to determine their origins.
Aid and assistance needed
Linear Mode
