I tried neck turning my 300 WM norma brass, before the mandrel it was .005-.001" runout on the neck, after the mandrel .004-.005", neck turned .004" run out. Am I using it wrong or does this happen to you?
Define "runout". Tough to tell what's going on unless you're more specific. Turning necks should not do anything to runout except to reduce it by the amount that the uneven neck thickness caused.
That's what I would have figured, but the expander mandrel is causing me .004" runout and the only way to possibly fix that is to fire form it, which to me is unexeptable. I would like runout to stay the same as the new case (.001") or better.