My two preferences are
Rottweil and my n/o1 choice brenneke usa
I also have 30 of those modified 50BMG cases on the way and 80 hard cast 1 O/Z Lee key slugs cast for 8% autonomy (by memory) Lee lead bricks.
I should be able to get them going damn fast out of those cases.
This isn’t going to be a half assed attempt with a box of 1O/Z Winchester Foster slugs as I do intend to walk away when I’m finished.