Seating Depth Comparator

Accuracy One Seating Depth Comparator

Accuracy One Seating Depth Comparator

The Accuracy One Seating Depth Comparator (SDC) measures bullet seating depth, ensuring consistency. The SDC is compatible with cartridges from 22 to 30 cal with .400” and larger shoulder diameter.

Seating Depth Comparator Features

  • Universal Design fits multiple cartridges.
  • Fast and convenient (Check every cartridge loaded in seconds)
  • Easy to use. (Push loaded cartridge into end of SDC and document reading)
  • Takes comparator number from cartridge case shoulder to bullet ogive.
Accuracy One Seating Depth Comparator with Cartridge

Measuring Seating Depth

Seating bullets to a consistent depth is a key part of producing quality handloads. How do you know if your bullets are seated to a consistent depth? There are a couple of ways to measure this.

Most tools made for measuring seating depth will give you a dimension from the cartridge base to a spot on the ogive of the seated bullet. What you really want to check is the distance from the shoulder of your case to the ogive of the seated bullet.

Why is that you ask?..

Well, when you fire a chambered cartridge, the strike from the firing pin first pushes the cartridge forward until it bottoms against the shoulder. The primer is then ignited. What this means is that your seated bullet depth consistency can more accurately be gauged using the dimension from shoulder to ogive. Using this dimension, you effectively eliminate any small variances in your sized case length from the equation.

Ease of Use and Cartridge Compatibility

The Accuracy One Seating Depth Comparator is designed to be fast to use. We offer an optional stand that allows mounting to a work surface for quick one handed operation. If you reload for several different cartridges, you won’t need additional adaptors. The Accuracy One Seating Depth Comparator is compatible with a wide array of cartridges from 22 caliber to 30.

In the interest of giving repeatable measurements and making our tool as universal as possible, the seats that contact the bullet and shoulder are radiused. Some other tools try to measure the bullet at the point it will contact the throat and even incorporate the 1.5 degree leade angle. This seems like a great idea, but we have found that it only results in sticky operation and dimensions that vary every time you try to take a measurement.

As a result of incorporating the radiused seats on the Accuracy One Seating Depth Comparator, the displayed measurement is to be used for comparison only

Using the Seating Depth Comparator

I will now give an example of use of the Comparator in conjunction with an OAL gauge.

Using the OAL gauge and case, I have gently seated a bullet into the lands, tightened the stop screw and carefully removed it from the chamber. Now I insert the bullet into the Seating Depth Comparator until the shoulder is seated in the opening of the tool. Zero the dial indicator. The tool is now zeroed at the lands.

A displayed positive number when checking a seated bullet from here would indicate a bullet seated into the lands, while a negative displayed number would indicate a bullet seated off of the lands. .010 would be .010 into the lands and -.010 would be .010 off of the lands. Alternatively, you may zero the dial indicator with no cartridge in the tool and use the number displayed when checking cartridges as a basis for comparison between many loaded cartridges.

Please note that displayed readings should only be used for comparison within a single lot of bullets.

Precision Primer Gauge and Seating Depth Comparator in Gauge Stand
The Precision Primer Gauge (Left) and Seating Depth Comparator (Right) shown in the Accuracy One Gauge Stand

Gauge Stand

The Accuracy One Gauge Stand is an optional add-on that is designed to accommodate both the Accuracy One Precision Primer Gauge and the Seating Depth Comparator. The stand is adjustable to any angle and allows for fast, convenient, one handed operation of the Precision Primer Gauge or Seating Depth Comparator.


  • SDC Without Indicator: $85.00
  • SDC With Indicator: $145.00
  • Gauge Stand: $55.00

How to Order

Orders can be placed via phone, email, or mail. Click below for ordering instructions.