You're overthinking the process. I'm also assuming that when you say "bullets", you're refering to the loaded cartridge.
What is important from a pressure aspect, is the volume of the case, not the overall length of the loaded round. Granted, the OAL will have an affect on volume, but if you measure the length of most brands of bullets, prior to loading them, you'll find some variation from one bullet to the next of the same weight bullet. Unless you're loading to the absolute maximum for the caliber, a small variation isn't going to hurt anything.
Your seating die should be setting the length of the loaded cartridge, so if you're having issues with some being shorter than others using the same weight and brand of bullet, it's probably due to the seating stem not matching the ogive of the bullet, and not allowing the tip of the bullet to bottom out on the seating stem.
If you want to check several bullets at one time, you can stand them in a row on a piece of flat glass, such as a mirror, and use a straight edge on top. That will tell you if any of them are shorter by looking under the straight edge.
Hope this helps.
Fred