Can you post a photo of the back side? Is the back side of the casting visible? Although there were plenty of Lord Admiral Nelson memorabilia pieces made, some of them are made with reclaimed/recast pieces of the ship. In the case of the HMS Victory, the original coppers from the hull of the ship were removed in the 1920's and were sold in small lots to fund the restoration and maintenance of the ship. I have a couple of items from different ships including two of Nelson's, Victory and Foudroyant. It is amazing to hold them and think of the action those pieces from the Victory saw. If you can access the back of the casting, you might be able to find some markings. A common one is B.F.S.S. which is British and Foreign Sailor's Society. which produced some of the commemorative centennial medalets and medallions.