7mm SWC Custom Build: End to End

7mm SWC can be the difference between being on target and off target in windy conditions. It also makes an incredibly compelling hunting cartridge. Watch the full video and read on to find out why!

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About the 7mm SWC

I recently outlined what I planned to do this year with Sherman Wildcat Cartridges. My first big project is a 7mm SWC build!

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.

It feeds from a .308 magazine without a binder plate. Maximum mag length is 2.960”.

This cartridge is still relatively new as it was first tested in April of 2024. I created the following cartridge diagram from a 3D CAD model.

Bill of Materials

Build Components for Upcoming 7mm SWC Build

BAT Machine’s Hammerhead was developed in concert with Unknown Munitions and features a shorter 75 degree bolt throw with different bolt stop options for different throw lengths.

It also shares the same tenon print as the BAT Igniter and BAT Bumblebee. I combined this tactical action with a Foundation Samson stock and Hawkins M5 DBM.

The Samson is composed of micarta with precision inletting and brass weights, making it incredibly versatile while not requiring bedding.

I selected the two-stage Bix’n Andy TacSport Pro-X Trigger from Bullet Central.

This trigger is extremely light and breaks like glass. For more info and TriggerScan results, check out our Bix’n Andy Trigger Shootout.

For the first time, I’m using a barrel blank from Custom Rifle Barrels (CRB). This is a 1 ¼” straight taper 1:8 7mm blank.

I’ll be chambering on my Precision Matthews PM-1440HVT-2 with reamers and gauges from Manson Precision.

As far as components, we’re starting with Alpha Munitions 7mm SWC brass from Sherman Wildcat Cartridges.

We have demonstrated multiple times the quality of Alpha’s OCD cases, in both precision and longevity. I have never had a primer pocket open up – something I cannot say about any other brass.

This is due to their Optimized Case Design (OCD) technology.

The full build will be topped off with an Element Optics Theos 6-36x56mm FFP scope.

About the PM-1440HVT-2

The Precision Matthews PM-1440HVT-2 is a great gunsmithing lathe, with the following stand-out features:

All Taiwanese built with Japanese spindle bearings
2.055″ thru-spindle capacity
Available cast iron ultra-rigid base
Variable Speed drive
14” Swing, 40” Between Centers
D1-5 Chuck Mount
MT3 Tailstock Taper

If you’d like to know more about the PM-1440HVT-2, check out our full overview HERE.

Machining

I started with the Hammerhead tenon print from BAT Machine.

This detailed resource provides all of the information needed without anything extra. Threads per inch are 1 1/16” x 18 and there is no counterbore.

The next step was to consult my chambering checklist to ensure I don’t miss any steps.

I keep a build spreadsheet I customize for each build that provides a flow for each of the critical dimensions.

Pre-Drilling the CRB on the PM-1440HVT-2

Single-Point Boring the Chamber Area True

I was very impressed with the 28” finished length barrel from Custom Rifle Barrels. It indicated very true regarding the concentricity of the OD of the barrel shank versus the concentricity of the lands and the grooves. As a result, I did not have to clock the barrel in an upward direction.

Gavin Chambering the 7mm SWC on the PM-1440HVT-2

Digital Depth Check for Cutting the Chamber

A borescope revealed a perfect chamber and throat area with a very even throat transition. This is indicative of the quality of the Manson Precision reamer.

Chambering with 7mm SWC Manson Precision Reamer

I finished off the barrel by laser engraving the details.

Putting It Together

I tightened the barrel to the receiver in a SAC Bravo vise, checking headspace before I torqued it down.

The ARCA section of the Arrow Products Rock Vise neatly held the Samson stock for easy barreled action installation.

Range Results

As always, I started at the 100-yard mid-mountain range.

There is no feeling that compares to great initial results with no load development. Three shots at 100 yards measured 0.159”.

I had loaded Berger 7mm 180 Grain Hybrid Target Bullets over Varget in virgin Alpha Munitions cases.

This bullet is one I consider “magic” that seems to always perform. I’ve had great results with it in 7 PRCW, 7mm PRC, and more.

Once on paper, I used some data Derek Webster from Sherman Wildcats had provided me to do a light load workup. I started with 39.7 grains of Varget, moved to 39.9 grains, and then to 40.1 grains, carefully recording chronograph data. All charges yielded impressive standard deviations.

I took the two most promising charges, 39.7 grains and 40.1 grains, and fired five-shot validation groups at 100 yards.

I had a flyer in the first five-shot group that may have come from the load or from human error.

Regardless, the 40.1 grain results were astounding. The five-shot group measured 0.189” with an average velocity of 2649.3 fps.

I loaded 40 more rounds of the same and headed to the ridgeline, hammering steel at 335 and 660 yards.

Shooting this rifle felt as though I was shooting the 6mm Dasher. Given, it does weigh 27 pounds so it is built to reduce recoil. I only shot prone, but shooting the rifle was smooth and predictable. I could easily see trace.

Encouraged by these results, I decided to engage Harold at 1390 yards. It took a few shots to get on target while navigating switching canyon winds, but I was successful two shots out of five. I was very happy with these results, given it was my first attempt and that this distance is much further than this PRS-focused cartridge is designed for.

7mm SWC vs. .280 AI

Working with the 7mm SWC felt oddly familiar. I soon realized it is essentially taking a .280 AI and making it short action.

While not possible with all cases, Alpha Munition’s OCD brass made it possible to run the 7mm SWC at near .280 AI velocities. I’m confident we can push it even further.

I observed 2649.3 fps with 7mm SWC from a 28” barrel. Hodgdon’s .280 AI data indicates 2,675 fps through a 24” barrel. Remember that the 7mm SWC is a short action and .280 AI is a long action cartridge!

Cartridge Comparisons

Considering a PRS scenario of engaging an 800 yard target in 8-12 mph winds, I ran calculations for 6mm Dasher, 6.5 Creedmoor, and 7mm SWC in Hornady 4DOF. I calculated wind holds for both ends of this range using a common load for each cartridge.

For the lightweight 6mm Dasher at 800 yards using a Berger 105 grain Hybrid, there is a variation of 0.68 MILs.

The 6.5 Creedmoor with a 140 Grain Hornady ELD-M bullet had a 0.58 MIL variation.

The 7mm SWC with a 190 grain Hornady A-Tip came in at a 0.48 MIL variation from 8 mph to 12 mph holdovers.

The above results indicate that 7mm SWC has 30% less switch wind variation from 8 to 12 mph than 6mm Dasher. This equates to 5.78” at 800 yards.

I also considered the total wind hold at 12 mph. The total wind hold percentages followed the same trends as those of the variation.

Once again, 7mm SWC emerged the winner. Where this takes practical effect is that a shooter would need to hold over less in the same winds with a 7mm SWC than a 6mm Dasher or 6.5 Creedmoor.

The more you have to hold over on your reticle, the more complicated your hold gets, the longer it takes to make the shot.

Conclusion

Though it’s always important to conduct further testing, I am excited at the potential of the 40.1 grain load and where I can go with 7mm SWC.

It is an inherently accurate cartridge with tremendous potential, particularly in the PRS world. Its better wind performance comes at the cost of greater recoil, which may not be for everyone, but is certainly worth investigating.

Even though this is a wildcat cartridge, Sherman Wildcat Cartridges has done a great job of working with the industry to ensure that reloaders and gunsmiths have the resources they need to work with 7mm SWC.