When shooting ctg. brass converted to bullets, anneal them totally, leaving the fired primer. At least, that is how I do this.

Huvius' idea of the .45ACP empty is a good one - if they are available at your range.

I agree that the proper size, in lead is the way to go. To paper patch a soft lead bullet, you would need around a .460" bullet to start with.

Friend of mine with a .500 BPE double used the pointy Lyman 450gr. bullet. Both his barrels would print into 8" at 100yards, but individual barrel groups were 2 1/2". He used a case of GOEX 3F black powder, card and lube wad as well, iirc.