After much experimentation and not a little soul searching, I have decided to up the maximum bullet weight allowed to 405 grains. Cast of wheelweights but no harder, can see no risk of target damage at BP velocitys. Not so with the 500 grainers, don't ask.
This should ease load development for those .45 caliber milspec rifles out there, and there are several good 350/375 slugs out there for the big 50s.