A new unfired cartridge case is approximately .002 shorter than minimum headspace, if you full length resize you will make the case shorter than necessary. If your headspace is .003 over minimum headspace you will push the shoulder back .005 every time you full length resize your cases and all you really need is to make it .001 to .002 shorter than your chamber.
REMEMBER, each time you full length resize your cases if you don't compensate for actual chamber headspace you are over resizing your cases.
The shell holders and headspace control shims below are made for full length resizing to only bump the shoulder of the case back .001 to .002.
You also have the controversy of partial full length resizing versus neck sizing only. Bottom line neck size only until the cases are a little hard to chamber and either use a bump die to push the should back or just partial full length resize enough to push the should back .001 to .002.
This applies to bolt action rifles only, if your loading for a semi-automatic you need to full length resize after each firing. (the minimum amount to chamber the round)
If you are really excessive compulsive you have a RCBS Precision Mic to measure your cases before and after firing.
Minimum rifle headspace.
New unfired cartridge, -.0015
Fired case, +.0013
NOTE: the photos above are 7.62 NATO cartridge cases and they are longer and thicker than a .308 Winchester cartridge case. New .308 Winchester cases are -.002 and when fired are +.003 due to the thinner brass case "in my rifle".
And now for grins and giggles guess which neck sizing die has the least amount of case runout.
http://www.youtube.com/watch?v=RZEas38vkKg
