With a 50 cal I don't see how you can use BMG bullets to be honest. If you are looking for a rifle that will shoot BIG bullets the obvious choice would be the .52 and paper patch sharps bullets. This mould throws a .512 bullet at 625 grains. Two wraps of 9# onion skin would put it at .518 and that would be snug not tight going down. They would load good, not move off the powder when carried. In my opinion it would be much more accurate with the right twist.

https://www.buffaloarms.com/Detail.a...95194&CAT=4158