Re: bullet seating depth
vette, set your dies to have them seat exactly where you want them, and just seat them once.
Seating them out further, and then seating a little more at a time does nothing for you but waste your time.
In regards to runout or concentricity, we refer to how concentric the bullet and/or case is. If a bullet is seated with runout, it hits the lands at an angle and the bullet then travels down the barrel off its axis.
Keep in mind, runout can sometimes be difficult to see just by looking at your loaded rounds.
If your afraid of differences in OAL i suggest you meplat trim all of your projectiles.
Provided you use good dies (which you are), the base to ogive length should remain the same or very very close to for all of your loaded rounds.
If you fiddle around with your dies on each seat, all you are doing is creating inconsistancy.