jradice45,
When you full-length resize the rifle case, not only are the walls pushed back into spec, but the shoulder is also being bumped back, depending on how you have your die adjusted. All that is really necessary is .002 - .003" adjustment from the fired case (make sure you measure cases fired in YOUR RIFLE!). This will prolong case life, as the shoulder is being worked less, and will also reduce the need for trimming, as the case is stretching less.
If you have a Hornady Lock N Load Headspace Gague
http://www.hornady.com/story.php?s=485
(halfway down), you can measure the headspace length of your chamber by measuring a case just fired in your rifle's chamber. Note what the headspace length is, then adjust your dies just so that, when you resize them, they now read about .002 - .003" less than the original measurement. My once-fired cases measure about 1.458", so I resize til they measure 1.455". Note that you can't measure this with just the calipers, due to the cartridge not headspacing to the case mouth, but the "datum line," a point on the shoulder that only the headspace gague can accurately and repeatibly find for you.
The point of all this is that, if you are pushing it back more - say .01" or more - then the neck is growing in length around that much longer each time you resize it (and the case wall, above the web, is growing proportionally THINNER each time, too! Case head separations happen quicker), and you've gotta trim off more than you normall would, as a result.
I'm gonna try to ASCII diagram this:
Here is a new case
==--------\___
Once fired
==----------\__
Has to be resized
=---------\______
Neck is too long - trim it!
=----------\__
Now imagine you bump the shoulder back WAY too far -
Once fired
==--------\___
Resized
-------\_________
Now see how much more trimming you have to do to get the case neck to the same length in relation to the over-all case length? (note that the equals signs at the back represent the web, which gets thinner as the firing / resizing cycle happens and the neck gets extended out and trimmed off - that trimmed brass has to come from SOMEWHERE if the rest of the case stays the same dimension!). Also consider that next time you fire it, that shoulder is going to have to stretch so far forward to fill the chamber, it may just pull the case wall from the web entirely and you will have a case head separation. Of course this is simplified, but I hope it helps illustrate the effects of resizing too far from both a brass life and trimming perspective.