It's a belgium or Spanish pinfire revolver
If you've on the cylinder a proofmark like ELG in a oval than the from Belgium
In a oval with a crown its after 1893 , without it's befor.
If you find a ELG you must also find a letter with a crown or star
Crown is before January 1877 , with a sar is after January 1877
If you find nothing of that than it's Spanish ...
Probably you can fire 12 mm pinfire cartridge.
Missing the grips of the butt and the éjection rod .
Got here a similar one in good shape ....clic on the link