.50 slug casting molds

One never knows until one shoots the cast product!
You have a Dragon Claw, yes? I see your recent post. I also see they recommend a .495 pellet or ball for that gun.
I just so happen to have a .500 Lyman Miniè "ball" (bullet) and a .500 roundball molds that I got as part of a larger purchase, and that I'll never use as I don't have a .500 gun. They may work. I'll sell them to you at whatever is the eBay going rate, and then if they don't work well, you can always resell on eBay.
Mike