What I did was take a 45-70 case and cut a slot in it down one side slightly longer than the seated bullet, and then I inserted a bullet into the slotted case, and set the overall COL. I took a marker and darkened the bullet nose so I could tell if it touched the lands, and then I would ream a little at a time and use the mock cartridge to check, and if it pushed the bullet down into the case after touching the lands, I knew I had to go a little deeper. Eventually after a couple of tries I arrived at the depth I wanted. Might not be the proper way of doing it, but that is how I did it.
