From tests done by buddy Roy Halpin of Texas, and myself, we have found the Lee Collet Die to consistently make ammunition with minimum run out when tested on a bullet / case spinner.
Bullet / case runout can be expected to be .000" to .003" when using the Lee Collet Die along with an in-line seater die from Bonanza or Redding. When using regular full length size dies or regular neck size dies, runout is usually twice that of what the Lee Collet die produces.
Why does the Lee Collet Die work so well? First, the Lee Collet Die is a neck sizer only. It reduces the diameter of the case neck by squeezing the case neck down against a mandrel using four "fingers". The end of the four "fingers" form a collar that is split into four segments. The four segments are forced into a taper, reducing the case neck to the shape of the round mandrel. Because brass is springy, the case neck springs back enough so that no case lube is required. Another plus is that neck to bullet tension can be varied by simply adjusting the die up or down. Rifle case necks require only a minimum amount of tension for the best accuracy (unlike pistol ammo, which requires a good crimp to create accuracy).
It has been entertaining to see RCBS and Lee bickering in the magazines about who owns green and the proper methods of reloading, but when it comes to neck sizing, the Lee Collet Die is my choice.