Building a Custom 6GT Rifle

I’ve been in the shooting business since the late 1990s. While there has always been a seemingly continuous rollout of new and better cartridges, it seems like the frequency of introductions has increased in the past few years. With an industry pivoting away from heavy caliber hunting rifles (I used to sell lots of 30-378 and 338-378 Weatherby’s when I worked the gun counter) towards precision rifles with light-recoiling, flat-shooting 6 and 6.5mm cartridges, it is hard to keep up with the latest trend. I believe it is safe to say, that in general, shooters want a cartridge with light-recoil, excellent external ballistics, and a case with inherent accuracy that feeds from an AICS style magazine.

Over the past decades I’ve covered many of these cartridges here. When the 308 Winchester feel out of favor for the 260 Remington, we saw the initial push towards 6.5mm. Other cartridges expanded these offerings, the 6.5×47 Lapua, 6.5 Creedmoor and the lighter hitting 6×47 Lapua and 6 Creedmoor took the precision shooting market by storm, with the 6.5 Creedmoor becoming the clear winner in the shooting community. I spent a lot of time with all of these cartridges, but was always enamored by the 6BR (and its larger cousin, the 6 Dasher). Known for unbelievable accuracy, this short and stout little cartridge didn’t feed well in AICS magazines and would often plague Remington 700 actions (and clones) with ejection problems due to its short case. If only someone made a 6BR (or 6 Dasher) that fed from a magazine and worked with most rifles. That is where the 6GT catches my attention.

Developed by George Gardner of GA Precision rifles and Tom Jacobs from Vapor Trail Bullets, the 6GT offers shooters a 105/107 grain class bullet with velocities around 3,000 feet/second; plus, it works from detachable magazines. In many ways it seems to be the perfect cartridge for the precision rifle match shooter. When my friend Billy Maxwell (from MaddMaxxGuns) wanted to make a new PRS rifle, he decided he wanted to build a 6GT, so that is what we are going to do in this post.

Before we get down to the machine work, it is important to take a few minutes to review the following disclaimer.

Before we get to the work, please take a look at the following disclaimer:

The contents of are produced for informational purposes only and should be performed by competent gunsmiths only. and its authors, do not assume any responsibility, directly or indirectly for the safety of the readers attempting to follow any instructions or perform any of the tasks shown, or the use or misuse of any information contained herein, on this website.

Any modifications made to a firearm should be made by a licensed gunsmith. Failure to do so may void warranties and result in an unsafe firearm and may cause injury or death.

Modifications to a firearm may result in personal injury or death, cause the firearm to not function properly, or malfunction, and cause the firearm to become unsafe.

For this build, I used the following items from Brownells:

For an action, I’m using a Remington 700 clone built by Stiller. Stiller makes some excellent stuff. This one is rebranded to another manufacturer, but is the equivalent of the TAC30 they currently produce.

For reference purposes, all lathe work for this project is going to be completed on my Precision Matthews PM-1440GT lathe, shown above.

Custom rifles always start with the barreled action. Since we are building on a custom Stiller action, no work is required to true or blueprint it. The barrel is a Bartlein Heavy Varmint 6mm 1:8″ twist in stainless-steel. This has a very heavy profile with a long, straight shank that makes for an excellent match rifle. Since the shank doesn’t have a taper, I decided to hold the breech end in my four-jaw chuck as opposed to my spider. There are a number of ways to hold and dial in a barrel. Over the years, I’ve found the type of barrel (such as length and contour) will often determine how you hold it.

I dial in the barrel as part of a multi-step process (not shown). When I initially mount the barrel, I use a dial indicator to dial it in concentric on the outside diameter of the muzzle and breech end; then, I face the breech end (which I had cut about an inch off of) and insert a ground “range rod” in the bore to indicate with on both ends. Once this is complete, I begin the machine work.

I use a high-speed steel 35-degree profile tool to cut the end of the barrel tenon to a diameter of 1.062″ inches. I like a light drag on the fit of the recoil lug when it passes over the tenon. Note, I’ve also cut a chamfer on the back end of the barrel.

Next I get the lathe set up for threading. I cut a groove where the tenon meets the back face of the recoil lug to mark the end of my thread passes with the lathe. Then, I set the lathe up for 16 threads per inch and use a high-speed steel threader to cut the threads.

As my threads begin to form, I’ll stop the lathe and check the fit against the action. One of the nice things about building a custom rifle is that you can make sure everything fits perfectly together.


A test fit shows everything aligns perfectly.

Like a Remington 700, a Stiller TAC30 requires a bolt nose recess cut. This can be made with either a form tool (shown above) or a boring bar. I can use either, but I think the form tool is slightly faster. In this case, I’m holding it in a floating reamer holder. To make the cut, I turn my spindle speed down to the lowest possible setting, insert the pilot from the form tool into the bore of the barrel, start the lathe and slowly drive the tool forward by turning the feed on the lathe’s tailstock quill.

To cut the chamber I’m using a live-pilot reamer and headspace gauge from Dave Manson at Manson Precision Reamers.

Somewhat foolishly, I forgot to take a picture of the reamer set up in the lathe. I held it in the same floating reamer holder shown above. When the chamber started coming to depth, I inserted the “go” gauge and screwed the action and bolt into place. I measure the gap of the tenon shoulder to determine how much deeper I needed to cut the chamber. As you close in on the final head space, I’ve found it pays to take your time and go slowly. If you take too deep of a cut you can create a condition that is difficult to resolve.

Once the chamber is cut, I chamfer the inside edge of the bolt nose recess. I do this with a boring bar. I simply insert it into the recess and slowly retract the compound on the lathe.

The chamber end of the rifle looks fantastic!

The finished barrel length on this rifle is going to be 26″. I made the initial cut on the bandsaw. This is a Powermatic 143 metal and wood cutting bandsaw, it is without a doubt on of my favorite machines in the shop.

To dial in the muzzle, I am using a spider attached to a face plate on the lathe. I dial in the outside diameter, make a facing cut and insert a range rod. I indicate off of the rod.

I use the same tools from the breech end to cut 5/8″-24 threads. I then hold the barrel in a vise and torque the action in place. Finally I check headspace one more time.

The finished rifle looks fantastic. Bill selected the MDT ACC chassis system, which, in my opinion, is the best option for today’s competitive shooter. The brake is the self-timing Area 419 Hellfire.

And his initial results look promising so far. These are both ten-shot groups. I’m thinking that I have a 6GT rifle in an ACC chassis in my future as well!