Yep - that's a pre-1893 proof so you're most the way there. You can always also wax cast the chambers and mic the casts, and slug the barrel, use those specs and refer to cartridges of the world for the most likely cartridge. (cartridges of the world is available in part online from google books)
After that present your findings to the CFC and request antique paperwork and you're golden. The pre-1893 proof is a great stamp to have on belgian guns - really makes your life easier and is recognized by the CFC.
After that present your findings to the CFC and request antique paperwork and you're golden. The pre-1893 proof is a great stamp to have on belgian guns - really makes your life easier and is recognized by the CFC.


















































