No. What you are describing is seated depth. The bearing surface is the portion of the bullet that contacts the valley of the grooves in the barrel. The parallel part of the bullet. If you rolled a bullet across an ink pad and then a piece of paper the bearing surface would be what left a black stripe on the paper.

To minimize run-out (bullet wobble) you want as much of that parallel portion supported by the neck as possible.

Check how you are using the Comparator. I have a .260 Rem (same case as the .308 but necked down) and my base-to-ogive runs from 2.263" to 2.287" (touching the lands) depending on bullet. Yours should be similar. My .260 has a pretty small leade (from what I am used to) and I have to seat much deeper than tha magazine would allow. But I'm not trying to max out speed so I don't mind. I am currently using a 0.015" jump and with the boat tail bullets I use the bases are at or below the widest part of the shoulder. So I set my seating die for 2.248" to 2.272" (base to ogive) depending on the bullet.

This link is Hornady's on using the Comparator: https://www.youtube.com/watch?v=3kL0HIgqqjU

Your Hornady #3031 is flat based and you shouldn't have much worry setting at a spot other than the channelure. Think of it as the Interlock ring to limit expansion rather than a crimp groove. I never crimp bolt action bullets in place and my 140 gr Hornady SST have the chanellure groove almost 3/16" ahead of the case mouth).


PS - when you say your "chamber" is 2.83" that is .003" longer that a "typical" loaded .308 Win round is from cartridge head to bullet tip. Your "chamber" should be 2.1835" (length of empty case) to the case mouth plus some leade of another 0.25"+/- until the ramp of the rifling starts. Since the bullet is pointed the part that doesn't contact the barrel wall is ignored for base-to-ogive measurements.