The PTG Bullet Comparator is designed to take measurements from the major diameter of a bullet to the case head rather than from the bullets tip to the case head. There are six holes that will work with each caliber listed in the description. Notes: Insert a cartridge into its correct size hole, then measure from the opposite face of the tool to the base of the cartridge. This dimension may be used to adjust seating dies so that the bullets are being seated more uniformly with respect to the bullet's ogive rather than a cartridge's overall length