All right! The revolver sounds very cool, I approve. The only thing I would change here is that the weapon wouldn't stop anyone who gets shot from casting magic. The bullets destroy spells that they hit, they don't prevent new spells from being cast. This does mean that they would go straight through any protection spells, so that could be bad news for witches.

Since the weapon is made of silver, it would incapacitate both vampires and fae. For everyone else, its effects would be the same as any other normal gun.