Hmmm....it's not likely to be a modern day nitro conversion from a BP muzzleloader: but remember that back in the 1870's, after Colt introduced its cartridge 1873 Peacemaker / Single Action Army, many percussion revolver owners had their pieces converted to fire these newfangled, self-contained cartridges.
How a 130 year old cartridge pistol fits in the UK's gun law scheme, I'm not sure. Is it treated like a modern cartridge pistol, because of its ignition system? Or is it accorded antique status, because of its age?
Anyone know?
Jim