Since I am a molly bullet shooter, the molly requires more tension; therefore, we use a bushing 0.003" smaller than total neck od. As to carbide expander buttons, please note this: if you are neck turning, NO expander ball! If you are not neck turning, use your carbide ball but verify your neck runout and thckness. Overbore
ps over time the brass will loose about 0.001" worth of tension as the brass will relax.
Member, Revolutionary War Veterans Association