Resolutions

Neck thickness is uniformed by neck turning.

Springback is lessened by heat treating. Relieving the non-uniform strain matrix in the brass makes it softer, and reduces springback.

The least runout will be achieved when the expander ball operation is skipped.

This is done simply by removing the decapping rod assembly from the full length sizing die. By necessity therefore, it will be necesary to obtain a universal decapping die, and a neck sizing mandrel. By mechanical design, the mandrel neck sizer induces the least runout. The Lee Collet Neck sizer is a sizing mandrel in a die, and a selection of manufacturers produce dedicated neck sizing mandrels.

Fitting the correct size seating stem that has the correct tolerance to the die body, and the correct cup profile to match your bullet ogive, will eliminate runout caused by bullet mis-alignment on seating.