I misspoke. The wiggle room is excess headspace. I have fixed that. It occurs with new cases, as they normally fit a chamber. That's what most folks start with. If you have some kind of parent to form down, then, of course, you have the option to start without excess headspace.
The bullet touching the lands, as I suggested, was to raise start pressure. No expectation it would prevent the primer driving the case forward to meet the headspace determinate. Just trying to get enough pressure before the bullet leaves the case so it seals the chamber against gas getting around the neck and shoulder. I'm presuming that's what has happened in the examples where his fireforming failed.
Gunsite Orange Hat Family Member
CMP Certified GSM Master Instructor
NRA Certified Rifle Instructor
NRA Benefactor Member