Adams & Lefaucheau pinfire revolver. Charles Fusnot, of Bruxelles, Belgium is the manufacturer of the cartridges: http://freemycollection.com/?page=manufacturers&id=17&name=Charles-Fusnot-Fabrique-de-Balles-et-Cartouches
Here are 4 variations of 12mm pinfire percussion adapters. These have a tapered “pin” to allow them to fit in an unmodified 12mm pinfire revolver. The screw on the bottom of the three, unscrews to allow cleaning by pushing something all the way through from the pin. These could be used with readily available caps and balls and powder when a supply of pinfire cartridges ran out.