You do not say what type of shotgun this is. Is it a muzzle loader, or is it a cartridge gun? The British gunmaker Westley Richards produced shotguns but I don't know if any of their products ended up in the hands of CW troops. The markings could be the maker, or maybe the original owner. Have you a photo of this weapon? If so, send me a copy via my e-mail and I will look at it.