How to Determine the Seating Depth of Bullets

Remove your gun's bolt and, using a firing pin removal tool, remove the firing pin by following the directions for your particular model of firing pin tool. Insert the bolt back into the gun.

Insert the bullet long in the shell, making it longer than the seating depth of the bullets you normally use. Turn the micrometer on top of your seating die to the length you are starting at for your bullet, and pull the handle of the seating die.

Insert the cartridge into the chamber, and attempt to close the bolt; a bolt that does not close indicates the bullet is too long. Remove your bullet and put it back in the seating die. Reduce the micrometer by five 1,000ths, and pull the seating die handle.

Place the newly seated bullet in the chamber, and if the bolt doesn't close, remove the cartridge and reduce the micrometer by another five 1,000ths.

Repeat this process of testing the bullet in the chamber and adjusting the seating depth, moving in increments of two 1,000ths and then one 1,000th as you get closer to the seating depth you are accustomed to using. When the bolt just barely fits past the bullet, you have a correctly sized bullet in the chamber.

Remove the bullet and insert into a bullet comparator, or calipers, to take a proper measurement of the bullet.

Repeat the bullet seating process with an additional two bullets, and measure each of them. Calculate the average measurement among the three to determine your seating depth.

Follow the instructions for your particular firing pin removal tool to return your firing pin to the gun.