Time to get your trusty vernier caliper out ( every reloaders owns one, right?)
Measure the neck OD of a fired case. Measure the neck OD of a sized case. Compare the two, any difference?
Measure the neck wall thickness (vernier calipers don't do a great job of this but will be near enough).
Subtract 2x the neck thickness from the sized neck OD.
Result should be around 2-3 thou less than a projectile OD (=0.221 - 0.222).
Excessively thin necks will give sloppy projectile fit as the dies will not be able to reduce the neck inside ID enough.
Shouldn't be a problem with factory brass though.
When pulling the expander ball back thru the neck does there seem to be any sizing occurring?
If you unscrew the expander ball/shaft will the expander slip back into the sized neck.
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