For the very first day of 2026 we present a precision rifle built with a modern 6mm cartridge — the 6GT. Developed by George Gardner of G.A. Precision and Tom Jacobs of Vapor Trail Bullets, the 6GT was designed to have the efficiency of a 6mm Dasher without the need for case forming. It was also designed with a longer case body so it feeds better from magazines. Even with the added capacity, the 6GT is still very efficient, and can achieve good velocities with less powder than a 6mm Creedmoor.

Today’s feature rifle was smithed and tested by Gavin Gear of UltimateReloader.com. Gavin did all the gunsmithing — chambering the barrel, fitting the muzzle brake, and even laser engraving the barrel. In building this 6GT rifle, Gavin used top-tier components: BAT TR action, Krieger 28″ 1:7.5″-twist 4-groove 6mm barrel, TriggerTech Diamond Rem 700-compatible trigger, and Area 419 Hellfire Muzzle Brake. The barreled action was then fitted in a handsome and rugged MDT ACC Chassis. On top is a Zero Tech 4.5-27×50mm FFP Trace Advanced scope in 30mm Hawkins Precision high rings.

We recommend you watch the video above — it covers the rifle build, load development, and then features some remarkable shooting sequences across snowy hills in the Pacific Northwest. Gavin’s team actually used a drone to capture overhead footage of the location.

After developing a promising load with Berger 109gr LRHT bullets, Varget powder, and Alpha brass, Gavin literally headed for the hills to test his new rifle at longer ranges, shooting from bipod. His load had shot well under half-MOA at 100 yards in testing so he was hoping he could hit multiple steel targets positioned at 340 yards, 760 yards, and 1000 yards. Indeed he did, proving the rifle’s great accuracy and Gavin’s fine trigger-pulling skills. You can see the hits at these time points in the above video:

340 Yards — 18:15 time | 760 Yards — 19:00 time | 1000 Yards — 19:54 Time

Gavin’s 6GT Hit Highlights on Steel out to 1000 Yards

Building Gavin’s 6GT Precision Rifle

Gavin Gear did all the gunsmithing on this project, using his own Precision Matthews TL-1660 lathe for the chambering with an Alpha carbide 6GT reamer. The barrel work took about four hours total. Shown below is the reamer cutting the chamber, which was finished with a 0.170″ freebore and 0.270″ neck diameter. For other brands of brass you might want the chamber to have a larger 0.272″ neck diameter.

Chambering the Krieger barrel with Alpha carbide 6GT reamer, 0.170” freebore, .270″ neck diameter.

This project when smoothly, with Gavin able to install the barreled action in the MDT Chassis and fit the buttstock in an hour or so. So total build time was about five hours. One nice “finishing touch” on the project was laser engraving the 28″ Krieger barrel — a process you can see in the video below.

Laser engraving of Krieger 28″ barrel.

About the 6GT — Sort of a 6 Dasher on Steroids

6GT Cartridge Design Features

The 6GT was designed to have an optimal length and capacity for mag-fed PRS/NRL tactical rifles. The 6GT is longer than a 6mmBR and 6 Dasher, but shorter than a 6mm Creedmoor and 6.5×47 Lapua. That gives the 6GT ample case body length to feed reliably from a magazine, while the case capacity is sufficient to run popular powders at reasonable pressures. It has a 35-degree shoulder angle.

On paper the 6GT seemed like the perfect cartridge for PRS- and NRL-style centerfire competition. It has the low recoil of a 6 Dasher, with good feeding and mag compatibility. With the 6GT, a competitor can push 6mm 105gr bullets at 3000+ FPS or run heavier bullets at ~2950 FPS. With this 28″ Krieger barrel, Gavin actually achieved 3004 FPS running 109gr Bergers.

On the G.A. Precision website, the qualities of the 6GT are listed as follows:

Loading for the 6GT

Gavin started with quality Alpha Munitions brass. The cases were then annealed with an AMP Annealer and trimmed to length with a Henderson powered trimmer (see video below). After sizing with a Forster Co-Ax press, Federal SR Primers were seated using a Primal Rights competition seater. Next the powder was measured with an A&D FX120i force restoration scale. Finally, the Berger 109gr LR Hybrid Target bullets were seated with a Forster Micrometer die, again using the smooth Forster Co-Ax press.

Initial Load Testing with Berger and Hornady Projectiles

Before it got cold and snowy, Gavin did load development, shooting from a bench with a Sinclair front rest. The Krieger cut-rifled barrel was accurate right from the start and Hodgdon Varget powder proved to be a very good choice for the 6GT.

Gavin’s 6GT boasts a MDT ACC short action chassis with SRS-X Elite buttstock, vertical grip, and MDT CKYE-POD Bipod.

Gavin did initial load testing with both Hornady 110gr A-Tip Match and Berger 109gr Long Range Hybrid Target bullets. The Berger 109gr LRHT bullets were the most promising. A variety of charge weights were tested, with Gavin settling on 34.6 grains of Varget. This delivered fine accuracy with a 3004 FPS muzzle velocity. Group size measurements with this load are shown in the chart. At 100 yards, four three-shot groups averaged 0.361 MOA, and the rifle produced a nice 0.387 MOA (0.405″) five-shot group.

The 6mm GT (aka 6GT) cartridge was conceived as a “bigger Dasher” for PRS and NRL competition. The 6mm GT’s creators wanted 6mm Dasher accuracy and moderate recoil delivered via a cartridge with a slightly longer case body for better mag-feeding, longer neck for seating flexibility, and more moderate pressures. So far the 6GT has performed very well in PRS competition. Today’s story is a bit different — this is about an experiment — running a 6mm GT in an F-TR type rifle. Understand that, under current NRA rules, you may only shoot .223 Rem (5.56×45) or .308 Win (7.62×51), in official, sanctioned F-TR competition, but the 6GT is fine for F-Open. Mike McCasland wanted to see the potential of the cartridge for long-range target shooting, so he put a 6mm GT-chambered Bartlein barrel on a nice custom rifle with McMillan XIT stock and Kelbly F-Class Panda action. The results were impressive.

6mm GT — New Cartridge with Multi-Discipline Potential

Story by Mike McCasland, Texas Precision
The 6mm GT began garnering attention within PRS circles in early 2019. It promised to shoot 105-110gr 6mm bullets at 2950-3000 FPS, yet not suffer from mag-feed issues sometimes found with 6mmBR variants such as the 6 Dasher, 6BRX, and 6BRA. Moreover, since it burned less powder, the 6mm GT promised increased barrel life compared to the 6mm Creedmoor or 6XC. The 6mm GT case size should still work with the accurate powders in the Varget burn-range. I found the 6GT also worked great with H4350.

As someone who aspired to building a repeater and jumping into the PRS game, and had a spare F-TR rifle sitting around, I thought it would be fun to build up a 6mm GT to see if there was any merit to the hype. My smith, Wes Ripley of RIP Precision in Texas, builds a lot of PRS rigs, and already had the reamer on hand (a 0.120″ freebore variant).

Whidden Gunworks had some 6mm GT FL bushing die kits in stock, so I figured why not see what all the fuss was about? At the very least I could play around with the 6mm GT in F-Open Class at local club matches to see how it compared to the 6BRA, 6 Dasher, and other popular 6mm cartridges.

Click image to see video comparison of multiple 6mm cartridges by Quarter Minute Magnums.

How the Project Got Started with Backup F-TR Rig
My 6mm GT build really started as a project spawned purely from COVID-19 Isolation boredom. This rifle primarily serves as a backup F-TR gun, and it had been relegated to performing some load development on .308 barrels, so I could spin new ones on my main match rifle. The only problem was, I had run out of .308 barrels that needed load development. So, I basically had an ideal test platform just collecting dust in the safe. All I needed was a 6mm GT-chambered barrel, since (like the 6mmBR) the 6mm GT works in a short action with a .308 Win-sized bolt-face.

About the 6mm GT Cartridge

BRASS — Editor’s Report: Lapua now offers excellent 6mm GT (aka 6GT) Lapua brass, product #4 PH6060C. You can also get very good Alpha Munitions 6mm GT brass and Peterson 6mm GT brass. Hornady produces 6mm GT brass as well, but we recommend Lapua, Alpha, or Peterson over Hornady. Lapua 6mm GT brass is in-stock now at Midsouth for $136.99/100 or Mile-High Shooting for $130.00/100. Alpha 6mm GT brass is available from K&M Precision for $130.00/100, and 500-ct bulk packs of Peterson 6mm GT Brass are available at Grafs.com for $548.14.

Mike McCasland reports: “I have used both Hornady and Alpha brass in this rifle and haven’t noticed much difference between the two. I will say that my batch of Alpha brass was slightly softer than Alpha brass I’ve used in other calibers; you could feel a difference when neck turning cases. I’m unsure if that’s a batch issue, or something specific to their 6mm GT brass as a whole. As far as performance, there was little discernable difference. Oddly enough, the Hornady brass seemed to have slightly less case capacity than the Alpha; with most other cartridges it’s the other way around.”

In this video, George Gardner of GA Precision talks about the 6mm GT cartridge which he helped develop.

POWDERS — The 6mm GT was designed with Hodgdon Varget in mind, and that popular powder works exceedingly well in this platform. That said, the 6mm GT can work with a wide variety of powders, some yielding better performance than Varget.

I’ve tried a multitude of powders during my initial 6mm GT load development: Varget, Shooters World Precision, RL16, VV N140, H4350, and RL-15 to name a few. In my barrel, Hodgdon H4350 seems to deliver the best velocity/accuracy combination. SD and ES also seemed to be the lowest with H4350.

Load Development for the 6mm GT — Many Powders Tested

BULLETS — The most common 0.120″ freebore chamber allows for the majority of high-BC 6mm projectiles found in both F-Class and PRS. I had good luck with the pointed 107gr Sierra Match Kings (SMK), as well as the 110gr Hornady A-Tips in my rifle. For those looking to run the heavier 112-115 grain 6mm offerings, I believe GAP designed a 0.160″ freebore reamer that gets those bullets out of the neck/shoulder junction. Shown below is the 0.120″ freebore JGS reamer print:

SUMMARY — Good Cartridge with Much Potential
Generally speaking, I think the 6mm GT is a good little round. Some may not subscribe to this theory, but I believe some cartridges are inherently easier to tune than others. I’m not sure the 6mm GT is as easy-to-tune as a 6mmBR, 6 Dasher, or 6 BRA, but I don’t think it lags that far behind.

With relatively little trouble, I was able to find loads with both Varget and H4350 that would consistently shoot very well — 0.2 to 0.3 MOA. Moreover, I found the 6GT cartridge lives up to the velocity claims made by G.A. Precision. I was easily able to push the 110gr A-Tips to 2950 FPS, and the 107gr SMKs to low 3000 FPS range without any pressure signs, or unnecessary wear and tear on the brass.

As a fun test, I ran my 6mm GT rifle in a local 1000-yard F-Class match with the 110gr A-Tips, just to see just how well they would perform. Although wind conditions of the day and some E-Target issues prevented my 6mm GT rig from getting the better of the larger 7mm and .30-Cal rifles, the 6mm GT proved itself an accurate little round at distance. Here is a 1000-yard ShotMarker target:

After putting several hundred rounds through my 6mm GT rifle, I anticipate building another 6GT on a repeater action to give PRS a try. I think if you are looking for a dual-purpose rifle that can run tactical matches (with 100% feeding reliability), and can also be used for mid-range, F-Open Class competition, the 6mm GT would be a very good option.

About the author, Mike McCasland:
Mike McCasland is an avid shooter who competes regularly in F-Class matches. Based in Texas, Mike is the creator of the Texas Precision YouTube Channel. There you’ll find many videos covering reloading, gun projects, and marksmanship. Mike has done some notable product reviews including a comparison test of Micrometer Competition Seating Dies. To access Mike’s YouTube Channel, CLICK HERE.

Big news — Lapua will be releasing 6mm GT and .300 WSM cartridge brass in 2024! Lapua has announced the addition of two major additions to its brass lineup. In spring, Lapua will start shipping .300 Winchester Short Magnum (WSM) cartridge cases. And, in the fall of 2024, Lapua promises to offer 6mm GT brass through authorized Lapua retailers.

Lapua 6mm GT (6GT) Brass

Lapua’s new 6mm GT brass promises to be a big hit with PRS/NRL shooters and varminters who want a bit more capacity than the 6mmBR case. The 6mm GT (aka 6GT) cartridge was conceived as a “bigger Dasher” for PRS/NRL competition. The 6mm GT’s creators wanted 6mm Dasher accuracy and moderate recoil delivered via a cartridge with a slightly longer case body for better mag-feeding, longer neck for seating flexibility, and more moderate pressures. So far the 6GT has performed very well in PRS/NRL competition. With the upcoming availability of premium Lapua-brand 6mm GT brass, we may also see a greater adoption of the 6GT in mid-range benchrest competition. We expect varminters may adopt the cartridge also, both in 6mm and necked down to .22 caliber.

Lapua’s Vice President of Sales & Marketing, Jarkko Aro stated, “Competitors shooting PRS, and similar long-range disciplines, have urged us to develop a 6mm GT case with unmatched quality and superior cartridge geometry to those currently offered in the marketplace. We’re confident we’ve exceeded their demands by collaborating with original cartridge developers, George Gardner and Tom Jacobs.”

Lapua .300 Winchester Short Magnum (WSM) Brass

Available in spring of 2024, Lapua will offer a superior-quality .300 WSM case through authorized retailers. Lapua cartridge cases are known for their superb quality, consistency, and longevity. Lapua brass cases are the #1 component choice of competitive shooters in most accuracy disciplines. Lapua uses only the highest-quality materials and manufacturing processes to satisfy the demands of reloaders who seek the highest levels of precision from their .300 WSM firearm platforms.

This product release is significant news for hunters and F-Open shooters. The .300 WSM has been an effective F-Open cartridge, both in .30-caliber and necked down to 7mm. With the availability of Lapua-brand .300 WSM brass later this spring, we expect that more F-Open shooters will employ a match cartridge based on this brass.

Lapua Sales & Marketing Manager, Erkki Seikkula stated, “.300 WSM reloading enthusiasts who insist on using the best components now have Lapua cartridge cases available for their long-range target rifles and custom hunting guns. From all of us at Lapua, thank you for seeking out our components to fulfill your precision reloading needs.” Order now for delivery in spring 2024 from authorized Lapua retailers.

For today’s Sunday GunDay story, we feature highlights from two in-depth reports on rifles built around the relatively new 6GT cartridge (also known as the “6mm GT”). Developed by George Gardner (G.A. Precision) and Tom Jacobs (Vapor Trail), the 6GT was designed to feed well from magazines, be more efficient than the 6mm Creedmoor, and offer outstanding accuracy. It is just enough bigger than the 6mmBR or 6 Dasher so it feeds better. But it retains many of the qualities of the 6mmBR (high efficiency and outstanding accuracy). Burning significantly less powder than the 6mm Creedmoor, the 6GT is a bit less expensive to shoot, and should, theoretically at least, deliver better barrel life.

“The [6GT] is a more predictable and barrel-friendly cartridge than the 6mm Creedmoor. It can utilize the accurate and forgiving powders of the 6BR, has fantastic accuracy, and due to its shoulder angle and case length, it doesn’t suffer from feeding issues.” — PewPewTactical.com

We should say that the 6 Dasher has been used very successfully in PRS/NRL competition, with some aftermarket magazine accessories. For this reason, if you already shoot a 6 Dasher, moving to a 6GT may not be worth the cost of new dies and new brass. A.J. Deysel, writing for LoadDevelopment.com, writes:

“The longer case of the 6mm GT means it feeds as reliably from a magazine as a 6mm Creedmoor, and offers slightly higher powder capacity and in turn velocities than the 6mmBR variants, whilst still being able to use the same accurate and forgiving propellants.

You will also find many competitive and average Joes shooting 6mmBR and 6mm Dashers with a Primal Rights or some other mag conversion kit, having very few if any mag-feed issues at all, so that pretty much also nullifies the need to move away from those [chamberings] if you already own one of those or the reloading equipment for it.” — LoadDevelopment.com

Part I: The 6GT Cartridge for Precision Rifle Competition

Report by Vu Pham
I was ready to build a 6 Dasher when I saw a lot of buzz… about a new caliber George Gardner (Owner of G.A. Precision) and Tom Jacobs (Owner of Vapor Trail Bullets) designed, the 6GT. After some research and talking to George, I ditched the 6mm Dasher build and had GA Precision build me a 6GT on a GAP Templar action I already had in the safe. The reasons to try the 6GT in a new PRS-style rig were as follows:

1. Push a 110-115 grain class bullet at 2880-2930 FPS safely in the Sacramento heat.

2. Achieve a load that is reliable and predictable. The caliber must be easy-to-tune and predictable from barrel to barrel. I don’t want to spend weeks developing a new load each time I spin on a fresh barrel.

3. Be able to run the same mag in all my guns without having to tweak or use mag kits. The round must feed from AICS and AW magazines without major tweaking or hiccups.

4. Get good barrel life. The barrel needs to go 2200-2500 rounds with match-grade reliability and accuracy.

5. Have a competitive cartridge with the least possible recoil without sacrificing too much performance down range, compared to bigger options like the 6mm Creedmoor.

6GT feeding from un-modified magazines has been flawless in all the rifles we tested. The 6GT feeds so well, I sometimes have to do a press check to ensure there is a round in the chamber.

On paper the 6GT seemed like the perfect cartridge for PRS- and NRL-style competition. It has the low recoil of a 6 Dasher, with good feeding and mag compatibility. With the 6GT, a competitor can push 105gr bullets at 3000+ FPS or run heavier bullets at 2800-2900+ FPS.

Knowing that I would initially have to make my own 6GT brass and do quite a bit of load development, I enlisted the help of Dan Bertocchini with CS Tactical. Dan has a lot more experience with wildcats and is the man when it comes to this type of data gathering. He has been running a 6 Dasher for a few years so I was curious how he would compare the 6GT to his 6 Dasher.

Quick Summary: “I am really digging the 6GT and the capabilities it offers. It can launch 103gr Vapor Trails at 3000+ FPS or lob heavy 115gr DTACs in the low-to-mid 2900s comfortably. I think we will see this cartridge go mainstream in PRS/NRL-style competition in 2020.” — Vu Pham

Alpha Munitions Pre-Production 6GT Brass
George Gardner was kind enough to send us 50 pieces of Pre-Production Alpha 6GT brass for preliminary testing. Like the cases I formed from 6.5×47 Lapua brass, the Alpha 6GT brass will use a small rifle primer. Purchased direct from Alpha Munitions, 6GT brass is now $1.30 per case, which is comparable with Lapua 6mm Creedmoor brass, currently $120.99/100 at Grafs.com.

The major difference between 6.5×47 Lapua-formed brass and Alpha 6GT brass is the case capacity. Alpha 6GT brass has 1.5 to 1.7 grains more case capacity. When a piece of 6.5×47 Lapua brass is formed into a 6GT, the walls of the case now become the shoulder and part of the neck. In a normal piece of brass, the shoulder and neck are typically thinner because of the thickness of the brass tapering from the body to neck.

While the cartridge design was optimized for Hodgdon Varget, the extra case capacity of the Alpha 6GT brass opens the door to Hodgdon H4350 (my favorite powder) and Alliant Reloder 16.

Test Results with Alpha Munitions 6GT Brass
Initial test results were as expected from a premium brass-maker. Dan and I both got excellent Standard Deviations and Extreme Spreads over my MagnetoSpeed V3 and his LabRadar. This string below was with 112gr Barnes Match Burners and 33.8 grains of Varget. Can’t complain about a 3 FPS Extreme Spread!

Yes, H4350 Works with the Alpha Munitions Brass
Personally, I prefer running Alpha 6GT brass with H4350 rather than Varget pushing a heavier bullet. H4350 burns slower and cleaner which should equate to better barrel life. The Lapua-formed 6GT cases just do not have the capacity to reach the cartridge’s full capability with the slower burning powders.

Is the 6GT cartridge accurate? Definitely. Here is a 5-shot group at 600 yards shot by Dan. This was Alpha 6GT brass, with Hodgdon H4350 pushing Barnes 112gr Match Burner bullets.

PART II — 6GT Load Development with Multiple Powders

This text is taken from a full report by Mike McCasland on his 6GT (aka “6mm GT”) bolt action rifle. This rig was designed for general use, not just for PRS/NRL matches. In his 6GT rifle, Mike tested multiple powders including Varget, H4350, Reloder 16, Reloder 15, Shooters World Precision, and Vihtavuori N140. For more details, CLICK HERE for full report.

About the 6mm GT Cartridge

BRASS — The first thing you’ll find is cartridge brass choices for the 6 GT are rather limited currently. At present, the only commercial options are Hornady and Alpha Munitions. For the die-hard Lapua fans, you can technically make 6mm GT brass from 6.5×47 Lapua, however that process is very labor-intensive.

I have used both Hornady and Alpha brass in this rifle and haven’t noticed much difference between the two. I will say that my batch of Alpha brass was slightly softer than Alpha brass I’ve used in other calibers; you could feel a difference when neck turning cases. I’m unsure if that’s a batch issue, or something specific to their 6mm GT brass as a whole. As far as performance, there was little discernable difference. Oddly enough, the Hornady brass seemed to have slightly less case capacity than the Alpha; with most other cartridges it’s the other way around.

POWDERS — The 6mm GT was designed with Hodgdon Varget in mind, and that popular powder works exceedingly well in this platform. That said, the 6mm GT can work with a wide variety of powders, some yielding better performance than Varget.

I’ve tried a multitude of powders during my initial 6mm GT load development: Varget, Shooters World Precision, RL16, VV N140, H4350, and RL-15 to name a few. In my barrel, Hodgdon H4350 seems to deliver the best velocity/accuracy combination. SD and ES also seemed to be the lowest with H4350.

Load Development for the 6mm GT — Many Powders Tested

BULLETS — The most common 0.120″ freebore chamber allows for the majority of high-BC 6mm projectiles found in both F-Class and PRS. I had good luck with the pointed 107gr Sierra Match Kings (SMK), as well as the 110gr Hornady A-Tips in my rifle. For those looking to run the heavier 112-115 grain 6mm offerings, I believe GAP designed a 0.160″ freebore reamer that gets those bullets out of the neck/shoulder junction. Shown below is the 0.120″ freebore JGS reamer print:

SUMMARY — Good Cartridge with Much Potential
Generally speaking, I think the 6mm GT is a good little round. Some may not subscribe to this theory, but I believe some cartridges are inherently easier to tune than others. I’m not sure the 6mm GT is as easy-to-tune as a 6mmBR, 6 Dasher, or 6 BRA, but I don’t think it lags that far behind.

With relatively little trouble, I was able to find loads with both Varget and H4350 that would consistently shoot very well — 0.2 to 0.3 MOA. Moreover, I found the 6GT cartridge lives up to the velocity claims made by G.A. Precision. I was easily able to push the 110gr A-Tips to 2950 FPS, and the 107gr SMKs to low 3000 FPS range without any pressure signs, or unnecessary wear and tear on the brass.

As a fun test, I ran my 6mm GT rifle in a local 1000-yard F-Class match with the 110gr A-Tips, just to see just how well they would perform. Although wind conditions of the day and some E-Target issues prevented my 6mm GT rig from getting the better of the larger 7mm and .30-Cal rifles, the 6mm GT proved itself an accurate little round at distance. Here is a 1000-yard ShotMarker target:

After putting several hundred rounds through my 6mm GT rifle, I anticipate building another 6GT on a repeater action to give PRS a try. I think if you are looking for a dual-purpose rifle that can run tactical matches (with 100% feeding reliability), and can also be used for mid-range, F-Open Class competition, the 6mm GT would be a very good option.

About the author, Mike McCasland:
Mike McCasland is an avid shooter who competes regularly in F-Class matches. Based in Texas, Mike is the creator of the Texas Precision YouTube Channel. There you’ll find many videos covering reloading, gun projects, and marksmanship. Mike has done some notable product reviews including a comparison test of Micrometer Competition Seating Dies. To access Mike’s YouTube Channel, CLICK HERE.

The 6mm GT (aka 6GT) cartridge was conceived as a “bigger Dasher” for PRS and NRL competition. The 6mm GT’s creators wanted 6mm Dasher accuracy and moderate recoil delivered via a cartridge with a slightly longer case body for better mag-feeding, longer neck for seating flexibility, and more moderate pressures. So far the 6GT has performed very well in PRS competition. Today’s story is a bit different — this is about an experiment — running a 6mm GT in an F-TR type rifle. Understand that, under current NRA rules, you may only shoot .223 Rem (5.56×45) or .308 Win (7.62×51), in official, sanctioned F-TR competition, but the 6GT is fine for F-Open. Mike McCasland wanted to see the potential of the cartridge for long-range target shooting, so he put a 6mm GT-chambered Bartlein barrel on a nice custom rifle with McMillan XIT stock and Kelbly F-Class Panda action. The results were impressive.

6mm GT — New Cartridge with Multi-Discipline Potential

Story by Mike McCasland, Texas Precision
The 6mm GT began garnering attention within PRS circles in early 2019. It promised to shoot 105-110gr 6mm bullets at 2950-3000 FPS, yet not suffer from mag-feed issues sometimes found with 6mmBR variants such as the 6 Dasher, 6BRX, and 6BRA. Moreover, since it burned less powder, the 6mm GT promised increased barrel life compared to the 6mm Creedmoor or 6XC. The 6mm GT case size should still work with the accurate powders in the Varget burn-range. I found the 6GT also worked great with H4350.

As someone who aspired to building a repeater and jumping into the PRS game, and had a spare F-TR rifle sitting around, I thought it would be fun to build up a 6mm GT to see if there was any merit to the hype. My smith, Wes Ripley of RIP Precision in Texas, builds a lot of PRS rigs, and already had the reamer on hand (a 0.120″ freebore variant).

Whidden Gunworks had some 6mm GT FL bushing die kits in stock, so I figured why not see what all the fuss was about? At the very least I could play around with the 6mm GT in F-Open Class at local club matches to see how it compared to the 6BRA, 6 Dasher, and other popular 6mm cartridges.

How the Project Got Started with Backup F-TR Rig
My 6mm GT build really started as a project spawned purely from COVID-19 Isolation boredom. This rifle primarily serves as a backup F-TR gun, and it had been relegated to performing some load development on .308 barrels, so I could spin new ones on my main match rifle. The only problem was, I had run out of .308 barrels that needed load development. So, I basically had an ideal test platform just collecting dust in the safe. All I needed was a 6mm GT-chambered barrel, since (like the 6mmBR) the 6mm GT works in a short action with a .308 Win-sized bolt-face.

About the 6mm GT Cartridge

BRASS — The first thing you’ll find is cartridge brass choices for the 6mmGT are rather limited currently. At present, the only commercial options are Hornady and Alpha Munitions. For the die-hard Lapua fans, you can technically make 6mm GT brass from 6.5×47 Lapua, however that process is very labor-intensive.

I have used both Hornady and Alpha brass in this rifle and haven’t noticed much difference between the two. I will say that my batch of Alpha brass was slightly softer than Alpha brass I’ve used in other calibers; you could feel a difference when neck turning cases. I’m unsure if that’s a batch issue, or something specific to their 6mm GT brass as a whole. As far as performance, there was little discernable difference. Oddly enough, the Hornady brass seemed to have slightly less case capacity than the Alpha; with most other cartridges it’s the other way around.

POWDERS — The 6mm GT was designed with Hodgdon Varget in mind, and that popular powder works exceedingly well in this platform. That said, the 6mm GT can work with a wide variety of powders, some yielding better performance than Varget.

I’ve tried a multitude of powders during my initial 6mm GT load development: Varget, Shooters World Precision, RL16, VV N140, H4350, and RL-15 to name a few. In my barrel, Hodgdon H4350 seems to deliver the best velocity/accuracy combination. SD and ES also seemed to be the lowest with H4350.

Load Development for the 6mm GT — Many Powders Tested

BULLETS — The most common 0.120″ freebore chamber allows for the majority of high-BC 6mm projectiles found in both F-Class and PRS. I had good luck with the pointed 107gr Sierra Match Kings (SMK), as well as the 110gr Hornady A-Tips in my rifle. For those looking to run the heavier 112-115 grain 6mm offerings, I believe GAP designed a 0.160″ freebore reamer that gets those bullets out of the neck/shoulder junction. Shown below is the 0.120″ freebore JGS reamer print:

SUMMARY — Good Cartridge with Much Potential
Generally speaking, I think the 6mm GT is a good little round. Some may not subscribe to this theory, but I believe some cartridges are inherently easier to tune than others. I’m not sure the 6mm GT is as easy-to-tune as a 6mmBR, 6 Dasher, or 6 BRA, but I don’t think it lags that far behind.

With relatively little trouble, I was able to find loads with both Varget and H4350 that would consistently shoot very well — 0.2 to 0.3 MOA. Moreover, I found the 6GT cartridge lives up to the velocity claims made by G.A. Precision. I was easily able to push the 110gr A-Tips to 2950 FPS, and the 107gr SMKs to low 3000 FPS range without any pressure signs, or unnecessary wear and tear on the brass.

As a fun test, I ran my 6mm GT rifle in a local 1000-yard F-Class match with the 110gr A-Tips, just to see just how well they would perform. Although wind conditions of the day and some E-Target issues prevented my 6mm GT rig from getting the better of the larger 7mm and .30-Cal rifles, the 6mm GT proved itself an accurate little round at distance. Here is a 1000-yard ShotMarker target:

After putting several hundred rounds through my 6mm GT rifle, I anticipate building another 6GT on a repeater action to give PRS a try. I think if you are looking for a dual-purpose rifle that can run tactical matches (with 100% feeding reliability), and can also be used for mid-range, F-Open Class competition, the 6mm GT would be a very good option.

About the author, Mike McCasland:
Mike McCasland is an avid shooter who competes regularly in F-Class matches. Based in Texas, Mike is the creator of the Texas Precision YouTube Channel. There you’ll find many videos covering reloading, gun projects, and marksmanship. Mike has done some notable product reviews including a comparison test of Micrometer Competition Seating Dies. To access Mike’s YouTube Channel, CLICK HERE.

Winchester has just introduced a new ball propellant, StaBALL 6.5, which it claims is very temp-stable. This means velocities and pressures should not vary greatly across a wide range of ambient temperatures. Winchester states: “StaBALL 6.5 is the world’s first temperature-insensitive Ball Powder, stable in extreme-hot or extreme-cold temperatures.” Winchester also claims StaBALL 6.5 can offer 30-200 fps greater velocities than other powders with similar burn rates. This new powder also has additives to reduce copper fouling. StaBALL 6.5’s burn rate and load density is good for popular cartridges such as .223 Rem, 6mm Creedmoor, 6.5×47 Lapua, 6.5 Creedmoor, and .270 Win. If StaBALL 6.5 can really deliver excellent metering, temp stability, more speed, AND less fouling — Winchester could really have a winner.

Metering Advantages of Ball Propellants
As there are existing very temp-stable extruded powders, such as Reloder 16 and H4350, what’s the big deal here? Well ball powders, with their small spherical granules, flow easily and meter well. This means ball powders can be thrown in manual powder measures with great precision. So StaBALL 6.5 could have advantages for hand-loaders using manual powder measures or progressive presses with mechanically-operated charge dispensers.

Reloading Data is ONLINE Now

Reloading Data is NOW Available on the Winchester website for a wide variety of cartridges including: 22 Nosler, .223 Rem, 224 Valkyrie, 22-250 Rem, 6GT, 6×47 Lapua, 6mm Creedmoor 6.5×47 Lapua, 6.5 Creedmoor, .260 Rem, .270 Win, 7mm-08, .30-06, 300 WSM and more. To get official LOAD DATA, scroll below the product description, select a cartridge type, and then click the RED “Get Reloading Data” tab. Here are two of 13 listed load options (55-115 grain bullets) for the 6mm Creedmoor:

Winchester’s StaBALL 6.5 Product Description States:

StaBALL 6.5 powder is available in 1 lb. and 8 lb. containers.

The New 6GT Cartridge for Precision Rifle Competition

Report by Vu Pham
Earlier this year I was ready to build a 6 Dasher when I saw a lot of buzz on the interwebs about a new caliber George Gardner (Owner of GA Precision) and Tom Jacobs (Owner of Vapor Trail Bullets) designed, the 6GT. After some research and talking to George, I ditched the 6mm Dasher build and had GA Precision build me a 6GT on a GAP Templar action I already had in the safe. The reasons to try the 6GT in a new PRS-style rig were as follows:

1. Push a 110-115 grain class bullet at 2880-2930 FPS safely in the Sacramento heat.

2. Achieve a load that is reliable and predictable. The caliber must be easy-to-tune and predictable from barrel to barrel. I don’t want to spend weeks developing a new load each time I spin on a fresh barrel.

3. Be able to run the same mag in all my guns without having to tweak or use mag kits. The round must feed from AICS and AW magazines without major tweaking or hiccups.

4. Get good barrel life. The barrel needs to go 2200-2500 rounds with match-grade reliability and accuracy.

5. Have a competitive cartridge with the least possible recoil without sacrificing too much performance down range, compared to bigger options like the 6mm Creedmoor.

6GT feeding from un-modified magazines has been flawless in all the rifles we tested. The 6GT feeds so well, I sometimes have to do a press check to ensure there is a round in the chamber.

On paper the 6GT seemed like the perfect cartridge for PRS- and NRL-style competition. It has the low recoil of a 6 Dasher, with good feeding and mag compatibility. With the 6GT, a competitor can push 105gr bullets at 3000+ FPS or run heavier bullets at 2800-2900+ FPS.

Knowing that I would initially have to make my own 6GT brass and do quite a bit of load development, I enlisted the help of Dan Bertocchini with CS Tactical. Dan has a lot more experience with wildcats and is the man when it comes to this type of data gathering. He has been running a 6 Dasher for a few years so I was curious how he would compare the 6GT to his 6 Dasher.

Quick Summary: “I am really digging the 6GT and the capabilities it offers. It can launch 103gr Vapor Trails at 3000+ FPS or lob heavy 115gr DTACs in the low-to-mid 2900s comfortably. I think we will see this cartridge go mainstream in PRS/NRL-style competition in 2020.” — Vu Pham

Alpha Munitions Pre-Production 6GT Brass
George Gardner was kind enough to send us 50 pieces of Pre-Production Alpha 6GT brass for preliminary testing. Like the cases I formed from 6.5×47 Lapua brass, the Alpha 6GT brass will use a small rifle primer. Price from Alpha Munitions should be $1.15 per case, which is on par with Alphan’s other product line.

The first 7000 pieces of Alpha 6GT brass sold before I could even get my hands on any! The bigger batch of production brass is due later this year. To pre-order the brass, CLICK HERE.

The major difference between 6.5×47 Lapua-formed brass and Alpha 6GT brass is the case capacity. Alpha 6GT brass has 1.5 to 1.7 grains more case capacity. When a piece of 6.5×47 Lapua brass is formed into a 6GT, the walls of the case now become the shoulder and part of the neck. In a normal piece of brass, the shoulder and neck are typically thinner because of the thickness of the brass tapering from the body to neck.

While the cartridge design was optimized for Hodgdon Varget, the extra case capacity of the Alpha 6GT brass opens the door to Hodgdon H4350 (my favorite powder) and Alliant Reloder 16.

Test Results with Alpha Munitions 6GT Brass
Initial test results were as expected from a premium brass-maker. Dan and I both got excellent Standard Deviations and Extreme Spreads over my MagnetoSpeed V3 and his LabRadar. This string below was with 112gr Barnes Match Burners and 33.8 grains of Varget. Can’t complain about a 3 FPS Extreme Spread!

Yes, H4350 Works with the Alpha Munitions Brass
Personally, I prefer running Alpha 6GT brass with H4350 rather than Varget pushing a heavier bullet. H4350 burns slower and cleaner which should equate to better barrel life. The Lapua-formed 6GT cases just do not have the capacity to reach the cartridge’s full capability with the slower burning powders.

Is the 6GT cartridge accurate? Definitely. Here is a 5-shot group at 600 yards shot by Dan. This was Alpha 6GT brass, with Hodgdon H4350 pushing Barnes 112gr Match Burner bullets.

And here is a 4-shot, 600-yard group with reformed 6.5×47 Lapua brass, using Varget powder under a Barnes 112gr Match Burner.

6GT Stress Test — Don’t Try this at Home!
Dan and I also did a “destruction test” to see how the Alpha 6GT brass would hold up when competitors push the cartridge to its limits. Please note that this is PRE-PRODUCTION brass and Dan and I probably exceeded max load for the majority of the duration of this test. Using Varget powder, we pushed 115gr DTACs at 2950+ FPS on a pretty hot day. We ran the charge weight up until the bolt was hard to lift.

Using this very hot charge, we were able to get 14 firings before the primer pocket failed. That is pretty solid considering that this brass was a pre-production sample that Alpha said did not meet its primer pocket design requirements. With these results, I think a shooter pushing 110-115 grain class bullets in the low 2900s will get 16 to 20 firings from a piece of brass.

Is the GT here to stay?
All signs are pointing to “Yes”. Dies are readily available from Hornady, RCBS, and Redding. Chamber reamers are being produced by PT&G and JGS that can be purchased through GA Precision.

Alpha Munitions is hard at work getting quality brass to the shooters. Quite a few people have already chambered up 6GT barrels before they even have brass in hand. I think we will see this cartridge go mainstream in PRS/NRL-style competition in 2020. With Alpha Munitions production brass almost ready to hit the shelves, I think we will see a lot more data come in from the field by the end of this year.

The Verdict — The 6GT Is Looking Great So Far
I am really digging the 6GT and the capabilities it offers. It can launch 103gr Vapor Trails at 3000+ FPS or lob heavy 115gr DTACs in the low to mid 2900s comfortably. George Gardner has texted me some pictures of very impressive groups pushing an 115gr DTAC at 3000 FPS with Alliant Reloder 16 (a very temp-stable powder with a burn rate close to H4350). That being said, if a guy wanted to push that type of speed and bullet weight, the 6mm Creedmoor is a better solution in my opinion. So far my “go to” 6GT load is a 112gr Barnes Match Burner at 2900 FPS. My other favorite load is a Hornady 108gr ELDM at 2970 FPS.

I think the down-range performance of the 6GT over a 6mmBR and the 6BR variants will be valuable on those days where shooting conditions are not as perfect. Recoil is about the same as the 6BR variants (6BRA, 6 Dasher etc.), but noticeably less than a 6mm Creedmoor. The extra energy down range will make a spotter’s job a bit easier when targets extend beyond 800 yards.

Forming GT Brass from Lapua 6.5×47
Before the new Alpha Munitions brass was available, I tested the cartridge using 6GT made from parent Lapua 6.5×47 Lapua brass necked-down and reformed. George Gardner walked me through the process of forming 6GT brass out of Lapua 6.5x47L. The process is time-consuming and is a huge PITA even with the correct tools. More detailed instructions can be found on my 6GT thread on the AccurateShooter Forum. READ Forum Thread HERE.

Here is a photo of what the brass looks like going through the forming/trimming process.
Left to right: 6.5×47 Lapua brass, sized with the 6GT bushing die with a .266 bushing, chopped/trimmed and turned, and fired-formed.

The formed-from-Lapua 6GT brass performed well and is a good option if one has the time and desire, but I’ll be moving over to factory Alpha Munitions brass once it is readily available.

6GT Tested at 1000 Yards
After seeing what Tom Jacobs is doing with his benchrest gun running Alpha Munitions brass, there is no doubt the 6GT is plenty capable out to 1000 yards and beyond. I have a feeling the Benchrest and F-Open guys are going to dig this new 6mm cartridge as well, at least for 600 yards. Note, in this photo it appears Shot #5 is under a paster, but that might just be a Ballistic-X software input error, meaning that this is actually a 4-shot group. Either way it is still impressive.