August 9th, 2020

Sunday GunDay: Texas Precision — Mike’s 6mm GT Rifle

mike mccasland 6mmGT 6 GT alpha brass 6BRA PRS F-Class

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.

mike mccasland 6mmGT 6 GT alpha brass 6BRA PRS F-ClassAs 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.

mike mccasland 6mmGT 6 GT alpha brass 6BRA PRS F-Class

6mm GT Rifle Specifications:

Action: Kelbly Panda F-Class SA RB/RP
Stock: McMillan XIT with RAD 2A
Barrel: 30″ 5R Bartlein 1:7.5″-Twist, HV Contour

Scope: Vortex Golden Eagle 15-60x52mm
Trigger: Jewell Benchrest, about 2 ounces
Bipod: Phoenix Precision

About the 6mm GT Cartridge

mike mccasland 6mmGT 6 GT alpha brass 6BRA PRS F-ClassBRASS — 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.

mike mccasland 6mmGT 6 GT alpha brass 6BRA PRS F-Class

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
mike mccasland 6mmGT 6 GT alpha brass 6BRA PRS F-Class

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:

mike mccasland 6mmGT 6 GT alpha brass 6BRA PRS F-Class

mike mccasland 6mmGT 6 GT alpha brass 6BRA PRS F-ClassSUMMARY — 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:

mike mccasland 6mmGT 6 GT alpha brass 6BRA PRS F-Class

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.

6mmGT 6 GT alpha brass mike mccasland PRS F-TR

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October 27th, 2019

New StaBALL 6.5 Powder from Winchester — Temp Stable

Winchester ball spherical propellant powder temperature stable staBALL 6.5

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.

Winchester ball spherical propellant powder temperature stable staBALL 6.5

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 ball spherical propellant powder temperature stable staBALL 6.5

Winchester’s StaBALL 6.5 Product Description States:

StaBALL 6.5 is the world’s first temperature-insensitive BALL® Powder, stable in extreme-hot or -cold conditions. It provides optimal loading density in cartridges appropriate for the burn speed, which is ideal for 6mm Creedmoor, 6GT, 6.5 Creedmoor, 7MM-08, .270 Winchester, and many more.

Typical of a ball powder, precise metering contributes to improved velocity and pressure standard deviations, ingredients that are paramount to match grade accuracy!

This “environmentally green” propellant has copper fouling reducer additives, meaning longer durations of competition and field shooting without having to clean the bore. Precision accuracy throughout the match!

Velocity levels obtainable, depending on the cartridge, are 30-200 fps greater than other propellants in its class.

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

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September 1st, 2019

Sunday GunDay: New 6GT Cartridge Tested in 3 Tactical Rifles

6GT Cartridge Alpha Munitions GA Precision PRS NRL brass 6.5x47 Lapua fire-formed neck-turn project

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 Cartridge Alpha Munitions GA Precision PRS NRL brass 6.5x47 Lapua fire-formed neck-turn project
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.

6GT Cartridge PRS NRL brass 6.5x47 Lapua 6GT 6mm Dasher cartridge fire-formed neck-turn project

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

The new 6GT Cartridge Was Tested in Three (3) Tactical Rifles:

Rifle 1: Vu’s 6GT 1.0
Builder: GA Precision
Action: Left Hand GAP Templar (large firing pin)
Barrel: Bartlein 7.7 Twist finished at 26″ with a 419 Hellfire Brake
Stock: KMW Sentinel
Optic: Vortex Razor Gen II 4.5-27x56mm EBR-7C MRAD
Bi-Pod: Harris
Trigger: Timney Calvin Elite
Magazines: AICS and AW
Support Bag: Wiebad Fortune Cookie

Rifle 2: Vu’s 6GT 2.0
Builder: Rubicon Precision
Action: Impact Precision 737
Barrel: Bartlein 7.0 Twist finished at 27″ with a 419 Hellfire Brake
Stock: XLR Industries Envy Chassis
Optic: Vortex Razor Gen II 4.5-27x56mm EBR-7C MRAD
Bi-Pod: Harris with Henderson Arca adapter
Trigger: Trigger Tech Diamond
Magazines: AICS and AW
Support Bag: Wiebad Fortune Cookie

Rifle 3: Dan’s 6GT
Builder: CS Tactical
Chambered by: Rubicon Precision
Action: Lone Peak Arms Fusion
Barrel: Proof 7.0 Twist finished at 28″ with a Muzzle Brake and More Brake
Stock: XLR Industries Envy Chassis
Optic: Minox ZP5 5-25x56mm MR4
Bi-Pod: Arca Cyke Pod (PRS)
Trigger: Trigger Tech Diamond
Magazines: MDT
Support Bag: Armageddon Gear OG Game Changer, Waxed Canvas

6GT Cartridge Alpha Munitions GA Precision LabRadar PRS NRL brass 6.5x47 Lapua fire-formed neck-turn project

Alpha Munitions Pre-Production 6GT Brass
6gt brass cartridge Alpha Munitions PRS 6mm DasherGeorge 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!

6GT Cartridge 600 yard target PRS NRL brass 6.5x47 Lapua fire-formed neck-turn project

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.

6GT Cartridge 600 yard target PRS NRL brass 6.5x47 Lapua fire-formed neck-turn project

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 Cartridge 600 yard target PRS NRL brass 6.5x47 Lapua fire-formed neck-turn project

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.

6GT Cartridge PRS NRL brass 6.5x47 Lapua fire-formed neck-turn project

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.

6GT Cartridge PRS NRL brass 6.5x47 Lapua fire-formed neck-turn project

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.

6GT Cartridge PRS NRL brass 6.5x47 Lapua fire-formed neck-turn project

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.

6GT Cartridge PRS NRL brass 6.5x47 Lapua fire-formed neck-turn project

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