Re: .260 rem COAL?
Sounds like you're on the right track. You are using the method I started out using and this will work good as long as the meplat and/or bullet tips are consistent (length).
A better method is the Hornady Load-N-Load O.A.L. Guage (straight for bolt action), the LNL Modified Case (.260 Rem) and the Hornady LNL Bullet Comparator (fits on digital caliper). You can get the Comparator and just the caliber insert (.264") you need or buy a Comparator and Basic set with 6 or 14 inserts. These kits are very handy if you reload for several calibers as I do. The kit with 6 inserts does not have .264. I bought this kit and added a .264 insert (much cheaper).
It is almost futile to try to obtain an accurate OAL for each bullet by measuring off the bullet tip. The tools I listed are for measuring off the bullet's ogive which will be more consistent and is the reference point used for measuring off the Lag's of your rifle's barrel.
The freebore in the chamber of my .260 (Remington 700 Mtn Rifle LSS) seems too shallow, but is probably factory/SAAMI specs. It's OK for the 100gn bullets but I wish it were a bit longer so as not to push the 120's and heavier so far back in the case. I usually try to keep all my loads .010" off the LaG. Hope this helps. JohnnyK.