Measuring cartridge lengths across the bullet tips is not a reliable (or repeatable) method for measuring loaded rounds. Its common for variations of up to .025 to exist from one round to the next. Our Bullet Comparator measures rounds from the ogive to provide consistent, precise measurements. You can also use it to check uniformity of bullets from base to ogive. Our Bullet Comparator easily attaches to the blade of your caliper and uses interchangeable inserts (available in sizes from .17 caliber to .45 caliber) to measure from the bullet ogive. Used in conjunction with the O.A.L. Gauge , the Bullet Comparator provides the ultimate in precision measurement. The Bullet Comparator will properly align the O.A.L. Gauge for precise measurement using a caliper. This method allows direct comparison of your loads as you set up your bullet seating die for any selected bullet free-travel (jump).