carbide sizing dies question

[Jack]

I agree that the expander ball is a significant factor. Not only can it pull the neck out of concentricity, it can also pull the shoulder forward.
Proper lubing of the inside of the case neck can prevent both.
IME, the benchrest type die that Redding makes with the interchangeable bushings will produce more concentric ammo.
A standard die, (either neck or FL) squeezes the neck more than needed, then opens it up again with the expander ball.
With the bench type die, you use the bushing you need to resize the neck only as much as you need to grip the bullet.
The benchrest type die is expensive- and probably more than you need for a hunting rifle. However, if you have a varmint/target rifle that's capable of very small groups, the bushing type die can help.