You need to invest in a quality micrometer AND a case trimmer. I would not reload without one. While you may not need to trim after every round, I would not fire a high powered rifle without knowing my case length. I've been out of reloading for a long time, and just got back into it. I would highly recomend the Lee case trimer. They are inexpensive, and VERY precise. I don't think it is possible to screw up your cases with one.
If you are not sure what to get, call Midway and those guys will help you out. I just resized 60 rounds of 22-250, and really liked how it worked. Also, make sure you get a chamfer tool and primer pocket cleaner if you don't own one. That will only set you back a few bucks as well...