Hello, I have recently inherited a SXS muzzleloading shotgun. I am told it was owned by my great-great grandfather (born 1828, died 1888). From what I could find easily is that the gun was Belgian made (Liege). It is in extremely rough shape so I'm not looking for value, just for a possible date or date range. The side plates and hammers are missing. The proof marks are on the bottom of the barrels. From what I can gather, I think it is 18mm bore with 17mm choke?The marks don't look exactly like what I've found on-line, but not sure if that is of any significance. Any information would be greatly appreciated. Thanks!