Wow, that is a beaut.
Mechanically, it is a copy of the Smith & Wesson Second Model .38 Single Action. Looks like the sideplate was replaced with a plain one.
Probably Spanish make, they liked to get sly references to American guns on their knockoffs.
Otherwise, neither Zhuk nor Google show the like.
I was able to find pictures of muzzleloaders with that ivory knob butt ascribed to the Caucasus. Obviously a continuation of the style into the breechloader era.
Note that it has no sights, like the muzzleloaders.