Hornady Lock N Load Comparator Set Body & 6 Inserts
Measuring cartridge lengths across the bullet tips is not a reliable (or repeatable) method for measuring you loaded rounds.  It's common for variations of up to .025" to exist from one round to the next.  Hornady's bullet comparator solves that problem by measuring rounds from a reliable surface on the bullet, the ogive, to provide consistent, precise measurements of your rounds.  Hornady's Bullet Comparator attaches to the blade of your caliper with a thumbscrew and uses interchangeable insert bushings to measure from the bullet ogive.  These bushings are available in fourteen sizes from .17 caliber to .45 caliber.  This set comes with inserts for following bullet diameters,  .224"(5.56mm), .243"(6mm), .257", .277", .284"(7mm), .308"(7.62 & 8mm)