Turn the necks on a couple and see what that does. As I've mentioned in previous threads, you can also remove the expander, size a few and check them. If you have little to no runout on those sized brass, then your expander is likely a cause of some of the runout.
I sent my sizer dies back to the manufacturer and had them hone the necks to where the OD of the sized brass is .002 less than a loaded round. No need for expander. No runout caused by die.