I have settled on the R P Tool 318-424-7867 firstname.lastname@example.org
shown here with the Hornady tool
It is a stainless rod with a brass tip with 2 locking collets. Well made and worth every penny of the $25.00 I paid for it 4 or 5 years ago.
You just insert the rod down to the bolt face (again make sure the firing pin is retracted) and lock the farthest collet
Retract the rod, remove the bolt and put a bullet to the lands, the Hornady makes an excellent tool to do this or you can use a dowel
Reinsert the rod to the tip of the bullet and lock the closest collet
Measure between the collets
The you can use that particular bullet to set the seating die with.
The advantage of this tool is that it gives you 2 hard clean surfaces to measure between and it will work with any gun any caliber. The most repeatable and foolproof system I have found.
Then all you have to worry about is the inconsistancies of the bullet ogives, the inconsistant seating depths that different bullet grips give, the inconsistant seating depths that different interior neck surfaces finishes give and how well your seating die is constructed.
EDITED TO ADD: I completely agree with this statement from boomtube
"You may not like the results of seating so close to the lands. Most factory rifles seem to prefer from .030" to four times that much jump. Many sporting rifle chambers won't even allow light-for-caliber bullets to be seated that far out.
Seating at, or even near, the lands is really a BR techique for use with their lightly held bullets. It makes up for their lack of any significant bullet pull/tension. Sporting ammo would likely come apart with routine handling if we load as the BR crowd does so loading long has little to offer us. AND, doing so can cause it's own problems. "