Steve,
To clarify, I don’t remove primers with the sizing die but instead use a universal decapper for that purpose. The reason I leave the expander stem loose is that I re-size without it in the die, then in an added step I re-install the stem and expand the necks on the upstroke of the case. I leave it loose thinking it will self-center as it goes into the case.
I too, use an old Lee decapping die that I bought in the dim times.
Just for fun, try tightening up the expander/decapping assy, decap with it, and check the runout. You don't have to do a lot, but based on what you said about 1 in 4 cases being excessive, try running 20 or so cases through and check the runout just using the one die. They should all measure the same. If they all measure 0.002, then your loose expander was the likely culprit. Problem solved.
![[Linked Image from i.imgur.com]](https://i.imgur.com/AP39Jhm.jpg)
