Last time I loaded 308 I was having to adjust my seating die every 2 or 3 cartridges. So after that session I ordered a micrometer seating plug for my die. Today I sat down to load with said plug for the first time. I also used same headstamp once fired brass that had been trimmed and sized. Even with the micrometer seating plug, I was getting variations of OAL of around 10 thousandths of an inch, with the OAL I was shooting for dead center of that 10 thousandths range. It was a real headscratcher, but since my finished cartridges all were well within saami spec for oal, I finished the tray I was making, then went downstairs to Google why. So I gather after Googling this that even same headstamp brass is going to give this issue when loading rifle cartridges. Funny that my 223 seems to all measure out the way I'd been doing it. Anyway, what I took from the forum posts I read about it is that I am just going to make myself crazy measuring base to tip like I have been. So I will order myself a Hornady comparator and anvil with a 308 insert to clip on my dial calipers. Would someone give me a quick rundown of how to properly measure this way? I am guessing I take one of my finished cartridges that is perfect in every dimension, throw it in the comparator, and then make all my 308 to that measurement. I gather this will give me cartridges that will still vary in tip to base oal, but will be within a couple thousandths from base to ogive. That sounds to me like I'd be making more consistent ammo. Still a novice guys, don't feel like you're talking down to me. I want to make the best quality ammo I can using the tools I have. Thanks!