Brief update.
Went to the range to try it out and fireform some brass.
Shot 5 PPU Hornet rounds, all split necks. Shot 4 Hornady 45 SP Match rounds, 2 split necks. Then I shot 19 into the group below. 18 formed perfectly, the one outlier split the case almost all the way to the base and landed far right. So that's 18 rounds using an old 8X weaver into a group measuring 1.034" out-to-out.