ORIGINAL: goatbrother
If the fire form loads have a headspace issue try using a 30 cal neck expander then when you neck down to .284" set the die so the case headspaces on the small shoulder formed from the 30 cal expander. A buddy has a 270 Gibbs, the case shoulder on that round is moved more forward than the Ackley improved and that is what they did to get the cases to fireform.
That's basically what I used to do to make .280 brass out of .270 Win. years ago when the .280 stuff was scarce........