A quick and easy way to measure and trim your cases, if used for general purpose shooting, is by use of Lee's trimmers. They will trim your cases to "Lee length" which is fine for most purposes outside match or long range varmint shooting. People refer to "LEE length" because in using this system you do not know just exactly where you have trimmed the case length unless you have calipers or other case measuring tools. Generally, those folks with calipers and etc. also have Wilson or Forster or other lathe type case trimmers. In addition, you may end up with cases which were too short for "LEE length"trimming, while most folks using the lathes will trim all the cases to equal the shortest one (within reason) in the bunch.
I have the Lee trimmers and I have a lathe trimmer and I use both. I can say that it has been my experience that the Lee trimmers work just fine when used on cases meant to shoot a deer in the brisket with a .30-30 or a .30-o6 or to bang the 200 yard 8" gong with my AR. Lee length may not work so well in my 6mmBR or 30BR which I require to shoot a lot tighter groups. Trimming to exact length for my AR does not seem to be an activity that results in any improved accuracy for me and is therefore a waste of my time. The same activity when used to produce cases for my .223 varmint rifle does seem to be worthwhile, resulting in tighter groups at 200 yards or more. I actually did do a side by side comparison of the two methods some years ago.
http://leeprecision.com/case-conditi...rimming-tools/
http://www.forsterproducts.com/catal...?prodid=700289