Complete Rebuild: Transforming a .308 Mossberg Patriot

I recently took apart Jim Harmer’s troublesome Mossberg Patriot just to take a look. I agreed it was the worst-performing bolt-action rifle I’d ever fired. Since then, I got to work and completely transformed it! 


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About the Rifle

Jim Harmer’s .308 Mossberg Patriot has given him issues for years. Even though it was returned to the factory, it still doesn’t shoot well. Something just isn’t right with it. I took some time to evaluate it.

My 100-yard group measured 3.8”, confirming Jim’s findings.

Gavin’s 100 Yard Results with the. 308 Mossberg Patriot

One peculiar feature of this rifle is the plastic “bottom metal.” It has corrugation on the bottom that sits directly on top of the stock.

Magwell Plastic Insert with Ribs

The action screws directly compress this area, which concerned me. I don’t believe this is conducive to accuracy. I also suspect the bore is bad. This meant a complete rebuild! (If you’re interested in learning hands-on gunsmithing, consider attending the Colorado School of Trades!)

Bill of Materials

Salvaging the action, I decided to change everything else on this rifle. OTM Tactical graciously sent along a 6mm 1:7.5 Krieger barrel blank for me to chamber in 6mm Dasher.

Abandoning the stock, I turned to an MDT LSS Gen 2 inletted for the Mossberg Patriot action along with their SCS buttstock and AICS magazines.

6mm Dasher doesn’t chamber from a .308 magazine, so I selected all metal 6BR magazines.

I also swapped the weaver mounts for a EGW 20 MOA Picatinny rail and added an ARCA rail with M-LOK on the bottom of the chassis. 

Barrel Work

The factory barrel measured 22” and was incredibly stubborn.

It took quite a bit of work to remove.

The action spun in the vise, so I started by adding heat before hitting it with a drift punch.

I eventually doubled my drywall tape in the SAC Bravo barrel vise and torqued it as much as possible.

I eventually had to hammer the action wrench until the action came loose. 

This two-lug design is similar to a Rem700 action, but with different threading. Overall, the barrel work went smoothly. I followed my traditional chambering process, starting with the breech end.

I dialed in the barrel on my Precision Matthews PM-1440HVT-2, then faced the tenon, turned the tenon, cut the thread relief, cut the shoulder, and threaded the barrel.

Cutting the Shoulder

Chambering came next.

I used a bandsaw to cut the barrel to my desired 26” finished length before essentially duplicating the work I did on the breech end.

I threaded the muzzle ⅝ x 24. 

Cerakote with Built American

I stripped the MDT LSS Gen 2 and SCS buttstock to their parts and placed everything I wanted to coat, including the magazines, in an acetone bath.

Next came sandblasting and cleaning off the parts before hanging them in my Built American DSBE-1500 spray booth. (Use UR5 to save 5% at Built American!) 

I mixed the Cerakote using a Cambridge Environmental A&J EJ-3000 balance and sprayed all the pieces with multicam dark grey Cerakote.

I tried a different spraying technique for the chassis, wrapping the buffer tube and using it as a handle rather than racking the chassis.

This gave me easy access to hard-to-reach areas. (I did have a screw in the end of the buffer tube to hang the chassis to dry.)

I also Cerakoted the barrel. For this project I used two BAE-0200 ovens.

I set one at 150 degrees Fahrenheit for the polymer and another at 250 Fahrenheit for the metal components.

Reassembly was easy with a Hex/Torx screwdriver set from Wheeler Tools

Putting it Together

Torquing the barrel onto the action was much easier than taking it off.

Chassis installation went smoothly.

This time I used the SAC modular barrel vise and a Wheeler F.A.T. wrench to mount the rails and Element Theos scope.

Eager to see how the rifle would perform, I shot it at 100 yards for comparison.

My first three-shot group measured 0.667” with Berger 109 grain bullets. The second measured 0.593”, but I pierced a primer and concluded the load was a bit too hot for the gun.

Switching to Berger 105 grain bullets and Varget, my next three-shot group measured 0.457” with no load development!

The rifle continued to display its accuracy on steel targets on the ridgeline but I did begin to have some ejection issues.

I polished the extractor claw and did some spring tuning on the ejection plunger after consulting Gordy Gritters.

So far I’ve had no further issues, but time will tell.


Though I only salvaged the action and transformed the .308 into a 6mm Dasher, there’s no question that the rifle is far better than the original. I was able to hit steel at 1,000 yards, something that would have been lucky to happen with the initial configuration. Now I just have to see what Jim thinks of the rebuild! 

If you’re interested in learning more about gunsmithing, consider attending the Colorado School of Trades. If not, consult a qualified gunsmith! 

Get the Gear

Colorado School of Trades

Shop barrels, actions, tools and more at OTM Tactical! (Use code UR5 to save 5%!)

Precision Matthews PM-1440HVT-2 Lathe 

Element Optics Theos 6-36×56 FFP 

Short Action Customs Barrel Vises

Use the code UR5 to save 5% sitewide on

Cambridge Environmental A&D EJ-3000

Wheeler Tools 65 Piece Hex/Torx Screwdriver Set

EGW Mossberg Patriot Tactical Scope Mount

Hodgdon Varget at Midsouth Shooters Supply

Berger 6mm 105 Grain Bullets at Creedmoor Sports

Longshot LR-3 2 Mile UHD – $899 MSRP

Longshot Hawk

Lyman Electronic Trigger Pull Gauge at Midsouth Shooters Supply

Ultimate Reloader Rifles

Garmin Xero C1 Pro at Creedmoor Sports and Midsouth Shooters Supply

Subscribe to @backfire on YouTube and to keep up with Jim’s adventures! 

Jim has also developed a cool recoil-reducing rifle buttpad called the Backstop. Check it out HERE.

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Gavin Gear

One thought on “Complete Rebuild: Transforming a .308 Mossberg Patriot”

  1. this article is just wasted, the viewers wanted to see you solve the issue not make a new rifle.

    It would have been better if you diagnosed the problem and solved them gradualy – change stock, straighten up the action etc in steps..

    not replace everything but the action..

    This was just a piece to make ad revenue for gear that noone in the targeted audience would even consider buyig.

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