It depends. Some .45 BHs are "convertibles", meaning they come with two cylinders - one for .45 Colt and one for .45 ACP. They should be marked but if not you can try to load a .45 Colt round. If it chambers you're good to go. If it doesn't fit you have a .45 ACP cylinder.
As far as what brand to use, Blackhawks are renowned for their strength, so you can shoot any commercial ammo in them.