Seating depth is a fine tuning variable. Start out with the bullet either in contact with the lands, or .005 off the lands. Find your powder and bullet like that, then play with seating depth to fine tune.
Edit: To elaborate a bit - I've not even experimented with seating depth in working up loads for the last several barrels I've worked with. Just started at .005 off with one, hard jam with another (VLD's), magazine length with another. Found acceptable accuracy there, and never "got around" to playing with seating depth at all. Seating depth DOES make a difference, but bullet and powder choice have a much greater influence on accuracy. I used to fine tune seating depth exhaustively, on every barrel, and found that almost all rifles shoot best with the bullet not more than .010 from the lands (most shoot better touching or only .005 off). So, anymore, I start out with what SHOULD be a good seating depth and worry about finding "the biggies" - bullet and powder. Only later, if I feel like it, or I'm not satisfied with the accuracy, will I fine tune with seating depth.
YMMV!
- DAA
