Proper length rounds are fundamental to accuracy.
Make precise measurements with this tool.

Comparator Body attaches to any caliper.
Measures cartridges from .17 to .45 caliber.

Measuring cartridge lengths across bullet tips is not a reliable or repeatable method for measuring your loaded rounds.
It' is not uncommon for variations of up to .025" to exist from one round to the next when measured across the bullet tips.
Bullet tips vary considerably due to the way in wich bullets are made.
Our 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.
The Bullet Comparator is also used to check uniformity of bullets, from base to ogive, wich is critical to accuracy.

The Bullet Comparator easily attaches to the blade of your caliper with a thumbscrew and uses interchangeable inserts to measure from the bullet ogive.
These bushings are available in fourteen sizes from .17 caliber to .45 caliber.

The basic set (B234) includes Comparator Body and 6 Inserts for bullet diameters included: .224" (5.56mm), .243" (6mm), .257", .277", .284" (7mm), .308" (7.62&8mm).

Bullet insert number and corresponding bullet caliber:
2-22 | .224" bullets
3-24 | .243" bullets
4-25 | .257" bullets
6-27 | .277" bullets
7-28 | .284" bullets
8-30 | .308" bullets

When used in conjunction with the OAL Gauge, the Bullet Comparator provides the ultimate in precision measurement.
The Bullet Comparator will properly align the OAL Gauge for proper, precise measurement using your caliper.
This methode allows direct comparison of your loads as you set up your bullet seating die for the correct bullet free travel (jump).

Instructions How to Use.
Attach Body to caliper with provided Thumb Screw.
The slot in the Comparator Body is machined to allow either "off-center" or "on-center" alignment with your caliper blade, depending on wich of the two threaded holes are employed.

When using the OAL (Over All Length) Gauge and Bullet Comparator in combination, always attach the Comparator Body to the "traveling" blade, in off-center position, then measure using the configuration shown in the illustration.
This method will align the OAL Gauge parallel to your caliper.
For all other uses the Comparator Body may be attached to either blade in the "on-center" position.

Place Bushing Insert (corresponding to bullet diameter) into Comparator Body.
Prior to measuring, close the caliper blades snugly on the Bushing Insert and Comparator Body, and tighten the Thumb Screw and Set Screw.
Then "zero" your caliper by setting the dial to "0" to achieve the same starting point in future measurements.
To take a reading, open the caliber blades, center the case-head (or bullet case) on the caliper's fixed blade and slowly close the caliper so that the bullet nose feeds into the Comparator until contact is made.
Be certain all surfaces are aligned and all slack is removed as light pressure is applied to caliper blades (be consistent).

When setting up your seating die compare your results (using measurements taken with the Bullet Comparator) with those from the OAL Gauge or a Dummy Round.
Remember that as you reduce the cartridge OAL from maximum the differance will be free-travel (jump) to the rifling.

Reducing bullet free-travel to closely match the chamber dimensions can provide significant improvements in accuracy.
However for hunting rounds we recommend that bullets are seated at least .020" of the rifling to ensure reliability in the field.

Remember: different bullets have different ogive curvature (i.e. #6 versus #10 ogive, and secant versus tangent ogive).
As a result the bullet free-travel (jump) may chenge as much as 1/16" or more when one bullet model is substituted for another.
Therefor a Comparator cannot be used to transfer dimensions from bullet "A" to bullet style "B" as this would be an apples and oranges comparison (the same reason the mic's, wich employ an imitation bullet, produce errant results).
When changing bullet models it is imperative to get new cartridge OAL dimensions from reloading reference material or from the firearm itself using a bullet seating depth gauge.
The best gauge for this purpose is Hornady's OAL Gauge.