1788 FM 2 Reale Mexico Silver Old Colony Treasure 1St U. The reign of Charles III. The Mexico City mint, opened in 1538, is still in operation. In 1783, The American Revolutionary War was won against. The British with the help of similar coins. Spain provided cash in. Of these very same Silver coins to the American patriots to. Support the war effort. Weight: 6.60 Grams, Fineness. Diameter: 28 mm, Mintage: Unknown. Thank You for looking. Be sure to add letsshop626 to your favorites list. Check out our other items.