The Hornady Bullet Comparators were designed to optimize comparisons between the base to ogive of bullets. We did design it so that it can also compare base to ogive of cartridges, but do to the large array of different cartridges we were not able to optimize the design to work with all cartridge base to ogive measurements. As a solution, our old bullet comparators are compatible with the Precision Measurement Station. We recommend using these for the cartridges whos case mouth bottoms out on the comparators included with the Precision Measurement Station. (.224,.243,.257,.264,.277,.284,.308).