I've been trying to figure out the readings I'm getting for my Ruger American 7mm-08. On some loads I did full-length sized, the reading is -2 thousandths before firing and between minus four to five thousandths fire formed. On some Hornady Americen Whitetail factory ammo, the rounds measure 0.000 before firing and between minus .001 and minus .002 afterward. Aren't the cases suposed to get longer so I can bump the shoulder back. I'm confused what would cause this.