Use a loaded, crimped round on the shellplate below the bullet seating die. The round must be crimped. At this stage, you should use a loaded round that has a bullet of the type you will be reloading, or the AOL may not end up correct.

This time with the loaded, crimped round in the seating die. If the round is not crimped, the next step may not give predictable results.

With the ram raised, and a loaded round in the die, screw the bullet seating screw until it meets the bullet. This is now the required AOL for reloading.

If the round is not crimped in this step, you'll screw the bullet seater all the way in without encountering any resistance, and end up with the bullet in the case below the case mouth.

Lower the ram, and clear the loaded round out of the way.