I acquired this from a collector in France (Thanks!)
Type: 12mm Horizontal Pinfire
Manufacturer: Jules Joseph Chaudun, Paris, France
Additional Info: This cartridge was most likely made by Jules Joseph Chaudun for some of the first centerfire (horizontal pinfire) guns Jean-Louis François Devisme made or converted. It was made somewhere around the late 1840s to 1850s. Chaudun would have probably labeled this as an 11mm cartridge.
(Fede, or JP, [or anyone] care to confirm or correct any of this?)
Here are the rest of the horizontal pinfires: http://www.freemycollection.com/?page=list_horizontalpinfire