6MM BR Custom Build – Hunt Report and Overview

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As a varmint hunter contemplating a new rifle build, you often run through a gamut of ideas that seem like a great idea, but don’t always end up in the final product.  I spent a great deal of time deciding what 6mm cartridge I would pick for my next varmint build.  I was sure of certain things.  First, it had to fit an action that I owned (Borden Alpine Magnum Medium Length Action) that was looking for a home.  Most importantly, it had to be highly accurate, with light recoil.  Quality, highly frangible bullets had to be available in the 50 to 70 grain weight range (for smaller to larger varmint hunting). For flat shooting ballistics, I wanted velocity above 3300 fps.  Lastly, it had to be a readily available cartridge. 


After a great deal of deliberation and weighing all the factors I listed above, I decided that the 6mm BR, with a slow twist barrel, was what I was looking for. This cartridge originally started out in 1978 as the 6mm Remington Bench Rest. In 1996 Norma modified the cartridge throat to accommodate longer, more efficient bullets. The rest is benchrest history. 

Every component for this build was carefully considered for the intended purpose. 

The Rifle Build:

Borden Alpine Magnum Medium Length Action (M700 footprint) 

Krieger Barrels M24 Contour 4R – .243” Stainless Steel Barrel – 1:10″ Twist – 26″ barrel

Grayboe Ridgeback Stock Hydrodipped in Kuiu by Applied Hydrographics

Grayboe M5 DBM Bottom Metal

Bix N’ Andy Dakota Remington 700 Trigger from Bullet Central – More information on this trigger HERE: https://www.varminter.com/the-bixn-andy-dakota-trigger-overview/

Vortex Razor HD LHT 3-15x42mm in MRAD

Seekins Precision 30mm Scope Rings

MK Machining Single Feed Ramp

Thunderbeast Ultra 9 – 6.5 Caliber Suppressor

Cerakote on Action, Barrel and Scope by Nevada Cerakote 

The chambering of this rifle was done by a local gunsmith and I assisted in the process. The Pacific Tool and Gauge Reamer cut flawlessly and the PTG Go and No-Go Gauges ensured our headspace was set properly. Once the barreled action was complete the Trigger Tech Trigger was installed and the assembly was placed into the Grayboe Ridgeback Stock. No modifications or adjustments were necessary and the rifle was ready to be topped with rings and the optics. The Seekins Precision rings and Vortex Razor HD LHT were torqued to factory specs and from there it was off to the reloading bench. 


Load Development:

As the desire to have a flat shooting was important I set my minimum velocity at 3300 fps. My brass choice was Lapua and always am thrilled when I end up with 101 pieces rather than 100. I used this extra piece to conduct destructive testing in my AMP Annealer to determine an AZTEC Code for later annealing. I did not resize or touch the brass before use.  I used Quickload to run various projectile and powder combinations and in the end decided on two variations. The bullets chosen were the Nosler 55 gr Varmageddon and the Hornady 58 gr V-Max. Both of these bullets are great choices and I wanted to see which one shot better in this build. 

Both of these bullets sit atop Vhitavouri N120 powder. The muzzle velocity was 3665 for the 55gr Varmageddon and 3426 fps for the 58gr V-Max. Both of these values were within 1% of the Quickload Modeled Velocity. Ten shot groups produced an SD in the low 20fps for both loads with the Nosler bullets

A Chronograph is a Must Have for Load & Ballistics Development

slightly beating out the Hornady with an average group of 0.36”. This rifle shot lights out! I was very impressed with the accuracy achieved, and remember the brass was new and was not resized. I am expecting to reduce group sizes with once fired brass and will provide updates in a future article. The only issue experienced with the build were feeding issues. This issue had nothing to do with the components or magazine, it is simply the port length on the Borden Alpine Magnum action is 2.75” versus a standard short action port length of 2.40”. This action was not recommended by Borden Accuracy for this build, it was simply an action that didn’t have a home, so I decided to use it for this rifle. The feeding issue occurs as the round clears the lip of the magazine it has not sufficiently entered the chamber, resulting in inconsistent feeding. The solution for this was an MK Machining single shot sled. No issues were observed after the first use of this sled.  

Hunt Report:

Now that all the hard work was over it was time to test the rifle in the field. I packed up my rifles and gear, newly reloaded Varmageddon bullets and headed East to meet the rest of the Varminter Crew (Cache Carlson and Eric Mayer) in Idaho to shoot some early spring rockchucks for a desperate landowner. 

The property we hunt in Idaho is loaded with rockchucks.  The rancher raises cattle, but also has a mixture of potatoes and beets growing on his property.  The pastures are surrounded by rimrock and brush.  This makes an ideal habitat for rockchucks to thrive.  With the protection of the rocks and the readily available vegetation for food, the numbers we found were shocking, explaining the landowner’s immediate need for help.

I was set-up on a shooting bench and was focused on the rockchucks living in the rimrock that bordered the main pasture where the land owner’s cows were feeding.  These rockchuck traveled about 200 yards to feed, then returned to disappear into holes dug under the rimrock.  The rockchucks were gathering in this area after their morning feed, to relax and soak up some sun before feeding again.  This made for excellent shot opportunities in the 100 to 400 yards range.

Springtime in Idaho means strong winds.  Shooting in rimrock, while the sun is out, means mirage.  Both of these factors made shooting rockchucks very challenging.  Even with these factors, I was able to connect on a decent number of ‘chucks. The accuracy of the 6BR cartridge, used in this build, was evident while shooting rockchucks at various ranges, in difficult conditions (see the video).  Clarity of some targets was also improved because the Vortex Razor rifle scope I was using provided edge-to-edge clarity and the 3-15 magnification was more than enough at the distances we were shooting. For closer shots, multiple rockchucks were able to be taken from the same area, due to the suppression capabilities of the Thunderbeast Ultra-9 suppressor. 

High winds can be murder on accuracy, but even as the wind picked-up, the 55 grain Nosler Varmageddon bullets, traveling at 3665 fps, still allowed for minimal windage adjustments.  Shorter flight time means less wind drift and the Nosler bullets proved to be devastating on the rockchucks.  Check out the video for the actual hunt and results!

Final Thoughts:

The 6BR Norma has not only proved itself as a premier benchrest cartridge but we can confirm, when used in a quality rifle build, it is a superior varmint cartridge as well. The rifle and cartridge were very accurate resulting in one shot kills throughout the hunt. There were times when my kill ratio was 100% over 7-8 shots in difficult shooting conditions.  The Nosler Varmageddon 55gr projectiles are a great match for this 6BR build.  They shot fantastic.  Resulting in quick, clean kills, which is our number one goal while hunting.  I will continue to use these projectiles in this build in the future.

David Hillis
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