HANDS-ON: Short Action Customs Modular Headspace Comparator Kit

The Short Action Custom Modular Headspace Comparator Set brings some bling that not only looks good but gives accurate data to the demanding reloader. In this story we’ll demonstrate both what’s included, and how it works!


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About the Short Action Customs Modular Headspace Comparator Kit and What’s in the Box

The Short Action Customs Modular Headspace Comparator Kit is a billet machined tray for holding two comparator bodies and insets/spaces for 12 modular inserts. Two modular comparator bodies are included, one long and one short. Four “modules” or inserts are also included in the kit. These four inserts are picked from an extensive list of cartridges and bullets diameters. This large list provides for the ability to match the exact neck and shoulder angle of the cartridge that are to be measured. Bullet comparators are even available to measure solid bullets if used. Versatility is designed into the two comparator bodies, both have the ability to be mounted centered or offset on the caliper blade. The offset ability allows for use of the Hornady COAL tool, very handy! This kit is very exacting, and precision measurements will be made easy. 

As a summary, here’s what’s included with the Short Action Custom Modular Headspace Comparator Set:

  • Billet Machined Storage Tray
  • Long Comparator Body
  • Short Comparator Body
  • 4 Modules/Inserts of your choice

Long and Short Bodies

The long body of the two allows room for measurements with a seated bullet in the cartridge. This configuration works with long loaded cartridges up to 338 Lapua Magnum with solid turned bullets.

Above: The long body being used to measure bullet seating depth

The short body of the two configurations is compact and is to be used when measuring fired brass or bullets only.

Headspace Comparator

The headspace modules are chosen based on the cartridge shoulder angle and bullet diameter. This design gives complete contact with the shoulder resulting in precise measurements. All of the modules are a simple snap in or out of the comparator body. The seating is positive and has no movement to affect measuring.

Bullet Comparator

The bullet comparator has an interesting tweak that I really like. The inside of the module has a 3 degree taper. This causes the bullet ogive-to-module interface to have a stable contact area, much more than just an edge. When placing a bullet in the module it seats in a stable manner. No guessing or wondering if you have the bullet in the correct position for measurement. Very nice design!

Comparison to other systems

The SAC Modular Headspace kit is a step up from its competitors. The fit and finish are excellent. Snapping the modular heads in and out is simple and repeatable. The modules interface with the bullet ogive or the brass shoulder surface areas is very solid and stable. There is no wobble or uncertainty if it is done correctly. The user can feel the solid interface. This leads to accurate reloading measurements.

In the video, we compared the Short Action Custom Modular Headspace Comparator Set to the following tools:


This is a great high end kit. It is very specific to each cartridge. If you have a wide collection or cartridges it is possible you will need to invest in multiple modules. At $30 each that can add up. However it could be worth it if you are a demanding and exacting reloader. The results are excellent from this kit. Invest in a pair of high quality digital calipers and this kit, and your measurements will be a level up!

Get Your Gear

You’ll find this comparator set on the Short Action Customs website:

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Travis Fox

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