Measuring cartridge lengths across the bullet tips is not a reliable (or repeatable) method of measuring the depth of set of loaded ammunition. It is common for variations of up to 0.025" to exist from one bullet to the next. Hornady's Bullet Comparator measures the cartridges from the breech to provide consistent, precise measurements. You can also use it to check the smoothness of the bullets from base (back) to bearing surface. Used in conjunction with the OAL Gauge, the Bullet Comparator provides the ultimate in precision measurement. The Bullet Comparator will adjust the OAL Meter for accurate measurement using a caliper. This method allows direct comparison of your charges when setting up the bullet seater die to get your desired free flight. The body that is used together with this can be found either in the Bullet comparator kit or in the headspace kit. Product Type: Brushes Brand: Hornady