I'm beginning to wonder if the brass was unevenly annealed at the factory. If so, running it into the sizer a couple more times will work work-harden it somewhat, evening it out.
The other possibility is that the rim thickness is a little uneven. This would tilt the cases as little as they're being pulled over the expander ball. It's beginni9ng to sound more and more like a brass problem.
Hmmm ... I do have a small quantity of once-fired Winchester brass from factory loads I could try. Will report back.
