The key to concentric 30 BR brass is expanding them up in several steps as not to push the should to one side or the other as the expansion process proceeds.
Using Elliptical neck expanders that have very little bearing surface ( less stress on the necks and brass), I step up to 25, 6.5 ,7mm and then 30 and then 30 cal expanding mandrel that matches my neck turner. The shoulder does and will move when sizing up the brass should be close to concentric when done correctly and ready to begin the neck turning process.
Neck turning can be done correctly before firing and should not need a final turning later if turned properly after the neck expansion process.
My .02¢.
DJ
DJ's Brass Service
Whose neck expanders do you recommend ? i was going to use the pma 6 to 30 expander . Do you use a cardbide expander?