Hi, Huttles, re : serial number, I personally would not be worried about the police knocking on your door. That grinding looks very old, I guess the gun was held up against a 'off hand' grinder [old school] not done with a modern angle grinder or dremel, see how the abrasion has over lapped on to the wood. this gun has probably changed hands several times since and been though auction, I doubt that the police would be the slightest bit interested. If it were mine I would try & blend in the flat area using files & emery cloth & re-stamp the number with letter/number punch's then blend in the shiny area to the old patina? not sure how but there will be somebody on here who knows? best regards Al.