Take out expander and use a mandrel die. Try turning bullet as you are seating unless you use an inline die. Measure before and after each operation so you can determine where run out was introduced. Things like Neck tension and neck wall thickness can also affect concentricity . Lube a bit...
That’s a great looking rig. I did that tone laminate with a Rem 700 LSS. Had sleeves installed in action, barrel and lugs lapped, bedding job . Now it shoots as good as a Sako. 👍