Bullet Comparator
A caliper insert that measures to a point on the bullet ogive rather than the tip, giving repeatable cartridge length readings for seating.
A bullet comparator is a small machined insert that clamps onto the jaw of a caliper and contacts the bullet at a fixed point on its ogive instead of at the soft, variable tip. Because bullet tips differ in length from one to the next, measuring overall length to the tip is unreliable, while measuring to the ogive is repeatable.
This lets the handloader record a consistent cartridge base to ogive figure, which is the number that actually governs how far the bullet sits from the rifling. Tracking that dimension is how reloaders set and reproduce a precise seating depth across a batch of ammunition.