Re: Trimming Case Length
I don't think a couple thousandths spread in a .308's case length makes any difference. They all get a bit shorter when fired, then lengthen a bit when full length sized; growing about 1/1000th inch for each shoot and resize cycle. Keep 'em between 2.000 and 2.010 inch and you won't notice any problems.
How the case mouth's prepped after trimming probably effects accuracy more than anything else. Best way to see if there's a problem is to view some rounds you've seated bullets in looking at the case mouth area through a magnifying glass. If there's bulet jacket peeling off the bullet as scraped by the case mouth, that bullet's now unbalanced. At 150,000 to 200,000 rpm a .308's bullet spins at, that's enough to cause problems. The case mouth's got a sharp edge that's shaving jacket material.
That's usually caused by regular deburring tools angle that leaves a sharp edge on the inside edge. I use a broken screw head Easy Out big enough to fit half way into a 30 caliber case mouth then spin it clockwise. That tool's shallower angle deburs and smooths out that sharp edge. Then I run all cases so prepped over a bore brush spinning in an electric drill. The end result's a nicely rounded inside of the case mouth. No more bullet jacket shaving. No more unbalanced bullets to start down your barrel.