I can't help much on the seating depth issue, but here is my experience with my .308.
The rifle is a Winchester model 70 heavy varmint with a 26" barrel that I bought used. I have a supply of Federal match ammo (168gr) that shoots very well and runs right at 2700fps in this rifle. I tried loading 168gr Sierra MK's at a similar velocity in an attempt to duplicate the accuracy. 45.0gr of Varget in R-P cases and Winchester WLR primers runs 2750fps and shoots a tad better. My testing has been mostly warm (80-90 degree) weather. Overall length is 2.845". This is as long as comfortably fits the magazine. My rifle was either chambered with generous freebore or the throat has eroded from previous use. I haven't tried to chase the lands and probably won't as long as it shoots well with magazine length rounds.