[DO NOT TRY THIS] Pushing 7 SWC To Magnum Levels

Here at Ultimate Reloader we’re all about data. We’ve shown a few pressure tests featuring Alpha Munitions Brass but are approaching this one with a new methodology. Follow along as we push Alpha Munitions 7mm SWC brass to the limit, but don’t try this at home!

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Methodology

John Miller, an engineer at DEWESoft, is joining me for this experiment as we work towards collecting data with some of their data acquisition solutions.

DEWESoft Sirius DAQ During the 50 BMG Pressure Testing

We’ve previously used their equipment to measure recoil, sound, and pressure.

6GT High Pressure Rig and Case Mouth Sensor Mounted on the Arrow Products Rock Vise

One of the advantages of using DEWESoft is how easy their software is to use. It allows us to see data in real time rather than scrubbing through Excel sheets at the conclusion of a test.

Alpha Munition’s OCD cases are known for their quality. I’ve demonstrated this multiple times, proving precision and longevity. I have never had a primer pocket open up – something I cannot say about any other brass.

In our “pushing .308 Win to .300 Win Mag” experiment we estimated pressures with QuickLoad. When we pushed 6GT to its limits, we drilled a hole through the barrel to collect pressure after the bullet went by.

This method wasn’t perfect as we lost some of the peak pressures and had to reverse engineer the data. This time, we’re collecting pressures in a non-destructive way!

John Miller explained that by using strain gauges, gauges that measure the deformation of an object when force is applied through changes in electrical resistance, there is no need to drill an otherwise unnecessary hole in a good barrel.

Preparing the Barrel for Strain Gauge Application, Sanding

The only negative is you have to strip the barrel to its raw materials. In other words, remove any coating and clean the barrel with acetone before applying the gauges.

Preparing the Barrel for Strain Gauge Application, Initial Clean with Acetone

In order to accurately calculate the pressure inside the vessel (barrel), we calibrated it using a hydraulic system.

Testing the Hydraulic Pump with Barrel Attached

Calibrating the Pressure in DEWESoftX with the Hydraulic Pump

About the Rifle

For this experiment, I am using my custom 7mm SWC.

7mm SWC or 7 SWC is a short action cartridge with magnum performance and a .308 bolt face, ideal for long, high BC 7mm bullets.

With a 40 degree shoulder the 7mm SWC has the appearance of an Ackley Improved cartridge and is optimized for bullets in the 180 to 195 grain range.

This rifle is centered around BAT Machine’s Hammerhead Action with a Foundation Samson Stock, Hawkins Precision M5 DBM, and Bix’n Andy TacSport PRO-X from Bullet Central.

I chambered a Custom Rifle Barrels blank on my Precision Matthews PM-1440HVT-2 with reamers and gauges from Manson Precision. I finished off this build with an Element Optics Theos 6-36x56mm FFP scope.

I had previously observed stellar accuracy in this rifle with the same components, Varget, Berger 7mm 180 Grain Hybrid Target Bullets, and Alpha Munitions brass.

Five shots at 100 yards with 40.1 grains of Varget measured 0.189” with an average velocity of 2649.3 fps.

Conducting the Test

I loaded a series of Alpha Munitions 7mm SWC cases with Varget under Berger 7mm 180 Grain Hybrid Target Bullets.

I loaded 10 cases in one grain increments, moving from 35.0 grains of Varget to 44.0 grains. We conducted this test in 100 degree weather but kept the ammunition out of direct sunlight.

I fired each round while John Miller watched the DEWESoft data stream and velocities on Athlon’s Rangecraft Velocity PRO Radar Chronograph.

After the first round of pressure testing, I hadn’t observed any signs of pressure, including stiff bolt lift, and we reached 2,626.6 fps. We decided to run the test a second time, this time loading up to 46.0 grains of Varget.

We sustained some ejector swipe with 46.0 grains of Varget and a pressure of 93,574 psi.

Results

We didn’t observe any pressure signs in the brass when we conducted our first round of testing with rounds ranging from 35.0 grains of Varget to 44.0 grains.

1st Round of Pressure Testing: 35.0 to 44.0 Grains of Varget

The second round of testing included the initial loads but also 45.0 grains and 46.0 grains of Varget.

2nd Round of Pressure Testing, 35 to 46 Grains of Varget

The velocities started at 2196.5 fps for 35.0 grains and increased to 2,782.8 fps with 46.0 grains.

Velocity Min & Max During 2nd Testing, 35 Grains and 44 Grains of Varget

I referenced data in the Hornady reloading manual and found that we met the capabilities of 7mm SAUM and were within 50 fps of the maximum load for 7mm Rem Mag with the 7mm SWC.

7mm SWC Velocities Reported from the Athlon Rangecraft

Keep in mind that the 7mm SWC short action utilizes a .308 bolt face, not a magnum bolt face like the 7mm SAUM! (The 7mm SAUM data was with a 175 grain bullet, not a 180 grain.)

7mm SWC Cartridge & Berger 180 Grain Hybrid Target

The pressure data revealed a starting pressure of 53,838 psi with 35.0 grains and an ending pressure of 93,574 psi with 46.0 grains.

At 46.0 grains we noticed a very slight impression of the ejector pocket and slight amount of swipe.

Alpha Brass After Firing with 35 Grains (Left) and 46 Grains (Right)

I’ve noticed this exact thing with multiple types of factory ammunition in cooler temperatures!

John Miller and I also discussed the validity of the data set, considering strain gauge locations as well as the calibration process.

We both agreed we’d like to revisit the calibration process but Miller pointed out that the relative differences between shots as well as the graphs indicated the data was accurate.

Conclusion

The combination of Alpha Munitions brass and 7mm SWC resulted in some impressive velocities and magnum performance near 7mm SAUM and 7mm Rem Mag.

We ran multiple strain gauges with one at the shoulder and one at the bore and would like to conduct two parallel tests in the future including different sensor locations and calibration processes.

Once again, Alpha Munitions brass allowed us to push the 7mm SWC further than we otherwise would and DEWESoft’s DAQ provided us a newer, cleaner data set. Remember, do NOT try this at home!