Hands-On: SAC Modular Sizing Die

Short Action Customs (SAC) is literally changing the game with their innovative products. In this story, we’ll take an in-depth look at the Short Action Customs Modular Sizing Die using 6 Dasher as an example. How is this die different than others? Read on to find out!

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About the SAC Modular Sizing Die

From the Short Action Customs Product Page:

THE NEW MODULAR SIZING DIES ARE USED FOR A FAMILY OF CARTRIDGES. THE DASHER DIE WORKS WITH 6 DASHER AND ALPHA 6 DASHER. EACH DIE IS SOLD WITH ONE NECK/SHOULDER BUSHING OF THE CUSTOMERS CHOICE. PLEASE BE SURE TO SELECT THE BUSHING YOU WOULD LIKE FROM THE MENU BEFORE YOU ADD THE DIE TO YOUR CART. IF YOU SELECT A 6MM NECK/SHOULDER BUSHING, BY DEFAULT YOUR MODULAR SIZING DIE WILL SHIP WITH A 6MM SOLID DECAPPING PIN.

“So why is this design any better?”

“The Modular Sizing Die” has a unique design where the cartridge’s body geometry is sized by the die body, the cartridge’s shoulder and neck geometry are sized by a “Neck/Shoulder Bushing”. This allows one die body to be used for the whole cartridge family.

Furthermore, the Modular Sizing Dies are precision machined with the main focus of properly sizing your fired brass. Our resizing dies will size the base of the cartridge slightly more than the shoulder.

After studying precision CNC machines and tooling, we designed the Precision Resizing Die to utilize a series of shallow tapers, not threads to properly center and secure the Solid Decapping Pin. Our tapered geometry offers unparalleled concentricity and repeatability.

Last but not least, we designed the cartridge sizing geometry to size a little more at the base and a little less at the shoulder when compared to most resizing dies on the market. In properly sized rifle chambers, this helps eliminate extraction issues of fired brass. Our shoulder sizing geometry helps minimize case runout and over working of the brass by not sizing the shoulder too much.

The design of this die sets it apart from other dies. Instead of being built on threads it is built on tapers. These tapers create a concentric geometry. This concentricity of the die contributes to minimum case neck runout.

The sizing die has an SAC specified salt nitride bath to help with lubricity.

The case body is sized by the die body while the neck and shoulder are sized by the bushing. Bushing insert is specific to your neck sizing demands.

Shoulder bump back is easy to adjust with the included shims. The die body stays in the press and the knurled top cap is removed. Shims are inserted between the neck bushing and the taper adaptor. Each shim provides 0.001 increase or decrease in the bump adjustment. With this adjustment configuration the die body stays in position to make full contact with the entire case. This keeps the entire case in line again helping contribute to the goal of reducing runout.

What’s In the Box

When you purchase your modular sizing die, you’ll get the following:

  • SAC sizing die body
  • Neck bushing of your choice 
  • Decapping pin 
  • Mandrel
  • Shims

It’s worth noting that the packaging is flat out amazing, as you’d expect from SAC!

Setting Up the SAC Modular Sizing Die

From the Short Action Customs Website: (see video for our demonstration)

To set up your Short Action Customs resizing die, please follow these steps:

  • Ensure the inside of the resizing die is clean and free of debris. We like to use a 40 caliber plastic pistol brush with a 12 ga. Shotgun patch to patch out the inside of the die body.
  • Select and install the appropriate shell holder. We headspaced our resizing dies to work with standard Redding or RCBS shell holders. Redding Competition Shell Holders as well as Forster Co-Ax press shell holders work well also.
  • With the reloading press ram all the way up, thread the resizing die into the top of the reloading press and continue to thread down until the die body touches the shell holder. Next, lower the ram and thread the die down slightly enough to achieve a little bit of “cam over” with the press. Tighten down the die body lock ring.
  • Then, using a headspace comparator that contacts the shoulder of the brass, establish the fired brass headspace. Next, lubricate a piece of clean, fired brass and cycle it through the Short Action Customs resizing die in a smooth, consistent ram stroke.
  • Then Measure your sized brass and compare it to the fired brass. We recommend reducing the headspace of the fired brass .001”-.002” for most shooting applications. In order to increase or decrease sized brass headspace. Thread the resizing die body into the press more, or less. The use of Redding Competition Shell Holders is also recommended. Another way to adjust headspace is to remove or install custom shims between the “Neck/Shoulder Bushing” and the “Taper Adapter”.

Using the headspace comparator to check shoulder bump:

Annealing the 6 Dasher Brass using AMP Mark II

Before sizing, the once-fired brass was annealed in the AMP Mark II induction annealer. This is worth noting because annealing your brass will reduce inconsistencies that you’d normally see with springback when bumping the shoulder while sizing.

6 Dasher Results

We had some AMAZING results with the SAC Modular Sizing Die!

Neck runout results shown on the Sinclair Concentricity Gauge were basically the same as with ground drill rod (the best case scenario, amazing). Shoulder bump consistency (as shown in the video) was exactly the same for 10 sized cases. These were checked with calipers capable of showing 0.0005″ difference.

This SAC Modular Sizing die combined with premium Alpha brass, annealed on the AMP Mark II concludes in top tier reloading results!  

In the next SAC feature, we’ll show how this sizer contributes to outstanding bullet seating results for runout, stay tuned!

Get the Gear

Here’s the gear used in this story:

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Thanks,
Travis Fox

One thought on “Hands-On: SAC Modular Sizing Die”

  1. I followed along and stayed with you with the exception of the individual die components but that’s what instructions are for. What I don’t understand is how you achieve these stellar results without first turning case necks to achieve uniform case wall thickness. The finished case might have zero run out but if case neck wall thickness varies the die will only move irregularities from the OD to the ID leaving unequal neck tension which also affects how cleanly the bullet leaves the case.

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