Grips appear to be hand-made/home-made replacements.
Flat firing pin on hammer indicates a rimfire cartridge.
The shape and length of the frame in the area behind the hammer and above the grips is somewhat unique.
Are the chambers bigger than a .22 rimfire round? Maybe .32 caliber (around .30" actual)?
Looks to be a Defender-type copy/clone. If it was made by one of the bigger-name companies of the mid-to-late 1800s, there would have been some markings, probably on the top of the frame above the cylinder. This is the closest thing I could find online:
Any guns of this type/era would be black-powder only; DO NOT try to shoot it with ANY modern ammo, even .22 Shorts or CBs.