I believe you'll be sizing the entire neck with the conventional die. Be sure to lube necks and pray the expander ball doesn't pull your nice chamber formed necks out of line on sizing. The Redding S style neck die will give you much more control of your neck tension and more concentric necks. Good Luck
lightbulbIf the expander/stem is giving high runout, or if you just want to safeguard a against it, don't tighten the stem nut down completely, leaving slight play in the stem.