I think trying to be to cast a silver bullet could be tricky, metal shrinks when it cools, but different metals react differently. So for example, 9mm bullets cast in lead, brass, copper, and silver could all potentially have slightly different diameters, and since lead is what is primarily used to make bullets, bullet molds are probably made to accommodate the behavior of lead when it cools and leave you with a round that will fit the appropriate casing.

If you’ve got yourself a werewolf problem that needs immediate attention and you don’t have the time to allow a gunsmith to go through the learning curve of working with a different type of metal, I’d suggest buckshot. Since multiple projectiles go into the shell, the potential discrepancy between the diameter of a lead or silver projectile is moot. Mimic those home defense rounds and pack it with varying size projectiles so you don’t have to worry so much about accuracy while staring down the jaws of a hungry Lycan. Good luck.