I think FLA shooter is doing just what he should be doing.
He can make a dummy round with 3.508 COAL(using drilled/measure bullet), then measure his MaxOgvOAL with a comparator like Sinclair's 'nut' & log it.
With this he has a reference point for his chamber with which to describe/log further seating adjustments.
He can go coarse seating adjustments to get in the ballpark, then go to fine adjustments to really dial in best grouping(as Berger recommends).
Optimum seating while not jammed can hold a wide window, or a very narrow window.
I have a Cooper in 223 that shoots 52gr Jayners at 8thou off the lands. 5thou, or 15thou, and you wouldn't think it was the same gun shooting.
I found this in 5thou adjustment steps(semi-coarse) as 10thou besting others. Then I dialed into 8thou and have been there for a long time, even with powder/primer changes.
It's mother of mystery to me, and for understanding of it, I would give up all things shooting and walk away content.