There's more than one way to skin a cat and this one calls out all the knives.
First of all, the optimum OAL with your bullet in your rifle with your load is subjective. NOT Absolute. Meaning we have to experiment and find the best combination for our individual circumstance and component selection.
OAL tools and comparators and precision mics are great tools, but not absolutely necessary to find the best OAL..........there's that absolute word again.
Those tools will sure help us reload ammo at a later date with different bullet lots to the same specs though.
Soot the bullet or mark the bullet with sharpie and seat deeper until barely noticable rifling marks show from chambering a previously fired dummy cartridge/case.......when satisfied, measure the OAL and call that "Jam".
Split the neck of a previously fired case and chamber the dummy round. measure just as above.....accomplishes the same thing but the bullet will move in/out of the case easier.
Barely resize the neck of a fired case (just enough to resist bullet movement by finger pressure) chamber and measure.......again, just like before, and easier than splitting a perfectly good case neck.
Using a once fired/fully neck sized case, seat the bullet deeper and deeper (gradually) untill you just, I mean just
faintly see rifling marks (polishing bullet with fine steel wool each attempt obviously)........at whatever seating depth you only faintly see marks, measure and call that "Jam".
Get a comparator, OAL tool, precision mic, use the cleaning rod method or any of the above methods and you'll get to the same place.........just use the same method every time you do it if you want repeatable results.
Start at point X and proceed to point Z; somewhere along the way, we'll find the optimum seating depth for that bullet/powder and charge/primer combo in that particular rifle.
Just remember, after a few hundred rounds fired; that relationship will change due to throat erosion of the lands. Then we gotta re-figure and adjust accordingly. This is obviously where the tools come in, cause we gotta measure and record all that again as the throat changes.....and again, and again, and again.........chase the lands, because they like to run from us.