I was wondering about this once so I did some checking on the ID of the comparators and the approx ID of the seating stem where it would hit the bullets. All of my comparators are .011" below caliber
Here is a 308 caliber comparator and it is .297" tight on the pin
Now seating stems probably vary quite a bit, but we all have observed that they seem to hit the bullet about halfway toward the tip. I only checked one since all my seaters are locked in and I don't want to take them apart, but the 308 seater die hits the bullet at approx .260"
so to me it would be more accurate to gauge your bullets as you seat them with the comparator and adjust your seating as you go along than to set your seater at one place and leave it there. Not to be anal about getting each bullet down to the .001" OAL but because during a string of bullet seating, connections on the press and dies can change slightly.