6GT current loads and progress

[6cmShooter]

Is the Hornady 6gt brass large or small rifle primers. I know alpha is small but can't find anything on the Hornady brass

 

[Oryx]

Hornady is small

 

[ghostrider_OneOne]

If anyone is interested in using H4831SC in the GT, here are some of my results with 115 RDFs (I have more of the 4831 powders than anything else, so I thought I would try it).

.020" jump
26" 7.5 twist Bartlein 5R HV (~850 rounds so far)
Hornady brass
Fed 205M
Rear bag and bipod off a bench. 3 mph 7 o'clock wind. 86 degrees F.

Did a 200 yard test of 38.5-40.5 grains if H4831SC (basing the loads on Hodgdon's 41.3 max. of Superformance for 110 grain A-Tip).
38.5, 39.0, and 39.5 were slightly crunchy; 40.0 and 40.5 were crunchy, but no pressure signs on any of these.
View attachment 7905981

39.5 looked good, so I loaded more of that and tried it at 200, 300, and 510 yards.
200 still looking good, 300 was so awesome I stopped after 3 shots (knowing the Random Damn Flyers were coming , and it opened up a bit at 510. I didn't chrono it, but based on the come-ups the velocity looks to be 2875-ish.

View attachment 7905982

View attachment 7905985

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Group size has little to no bearing no effectiveness of this ignition combination. How about some data with with ES, SD, and sample size.
Group size can be optimized with tuner and/or seating depth.

 

[Professor Oblivion]

Group size has little to no bearing no effectiveness of this ignition combination. How about some data with with ES, SD, and sample size.
Group size can be optimized with tuner and/or seating depth.

Sorry, I completely forgot that I did shoot a five-shot string of the 39.5 load over a chronograph at 100 yards a few weeks later. Not the greatest sample size for sure, and yep, doing it assbackwards as usual .

Velocity
2852 Average 2848
2836 High 2855
2849 Low 2836
2850 ES 19
2855 SD 7.30

Looking at my notes, the temp for the day I shot the groups was 86F and the day I shot for velocity was 87F, so I am not sure what was causing the slowdown.

 

[ghostrider_OneOne]

It can. In cases where other prerequisites have been met. In cases where a powder just isn't going to work, seating depth (or tuners) can't fix everything. Don't get confused by the Cortnia

Sorry, I completely forgot that I did shoot a five-shot string of the 39.5 load over a chronograph at 100 yards a few weeks later. Not the greatest sample size for sure, and yep, doing it assbackwards as usual .

Velocity
2852 Average 2848
2836 High
2849 Low 2836
2850 ES 19
2855 SD 7.30

Looking at my notes, the temp for the day I shot the groups was 86F and the day I shot for velocity was 87F, so I am not sure what was causing the slowdown.

Thanks, very helpful!

Sorry, I completely forgot that I did shoot a five-shot string of the 39.5 load over a chronograph at 100 yards a few weeks later. Not the greatest sample size for sure, and yep, doing it assbackwards as usual .

Velocity
2852 Average 2848
2836 High 2855
2849 Low 2836
2850 ES 19
2855 SD 7.30

Looking at my notes, the temp for the day I shot the groups was 86F and the day I shot for velocity was 87F, so I am not sure what was causing the slowdown.

Thank you! That helps

 

[gorillamotors]

Hello,
Just took delivery of my new GAP 6GT. Lots of great information here on loading for the cartridge wanted to take the opportunity to say thanks for the information in advance. I have also seen questions regarding color choices on the forun so thought I would include a couple pics for reference. GAP did a fantastic job on this rifle and I am very excited to shoot this beauty for the first time. Paint is Scorched Earth and looks fantastic in person, much nicer than I expected. So far I have Varget, Alpha brass, two types of projectiles (105gr Nosler RDF and 110 Hornady A-Tip's). Time to break this bad boy in.
Happy new year everyone

What rifle case is that?

 

[gorillamotors]

What is the parent case for the 6GT or is there any?

 

[NiteQwill]

What is the parent case for the 6GT or is there any?

6.5x47 Lapua necked down

 

[insertusernamehere]

Never mind, just found the massive 6GT thread

 

[Ozman]

Sorry I forgot this on my original post. I loaded up a couple dummy rounds for seating depth on the K&M Arbor press and the neck tension was about 35 to 40lbs on this new brass. I used a mandrel to ensure consistency of the necks in the new alpha brass. Does anyone have any insight if this is about normal or what value we should be aiming for for neck tension when seating?
Thanks everyone.

This is an old post, but I will tell others what works great for me with brand new Alpha 6GT brass (currently $130/100 at GAP as of 2/2024):

1. Use a mandrel or expander if you want something different than the factory tension…I personally use a .241 expander, which springs back to .2405ish

2. Next, the critical step: dry tumble the new brass for 90 minutes or so with a bit of brass polish added to your media…this seems to add just enough lube inside of the neck to overcome the friction of the factory new brass [this suggestion comes second hand direct from Alpha customer service]

3. Finally, I DO chamfer the new brass…try it with or without, but it makes for more consistent seating.

Let me hear your feedback…the Alpha 6GT brass is definitely a bit more stout than the Hornady brass.

 

[Black Greyhound]

Keeping this thread going... Anyone else using Vitavourhi powder in their 6GT. My rifle shoots great with RL TS15.5 (see 200 yd target below) and Varget, but the Vit powders are SO much less expensive, I'm wondering if it's worth giving them a try. For background I'm using Fed 205M primers,, Alpha brass and Berger 105 hybrids though a 26", 1:7.5 barrel.

 

[NiteQwill]

Keeping this thread going... Anyone else using Vitavourhi powder in their 6GT. My rifle shoots great with RL TS15.5 (see 200 yd target below) and Varget, but the Vit powders are SO much less expensive, I'm wondering if it's worth giving them a try. For background I'm using Fed 205M primers,, Alpha brass and Berger 105 hybrids though a 26", 1:7.5 barrel.

N140 is a great Varget substitute. It will run fine (and cleaner IMHO).

 

[Black Greyhound]

N140 is a great Varget substitute. It will run fine (and cleaner IMHO).

Temp stability?

 

[NiteQwill]

Temp stability?

Very temp table

 

[Kocher]

Just a thought as I’ve noticed, I couldn’t find anybody talking about the max pressure differences between the GT and the BR style 6 mm’s run at:

piercing primers with the CCI 400s

6 GT runs at 62,000 psi
6 Dasher runs at 52,000 Psi.

The CCI 400s have given me trouble even in the 6arc max charges seems like the CCI 400s are more susceptible. Depth that your firing pen goes may also affect this..

Thought I would pick up a 6mGT or dasher, but I’ve got some Creedmoor barrels that are not used up and I’ve yet to hardly run those so be silly me to get another cartridge.. not to mention all the 6 CM federal brass I picked up on the cheap…. or perhaps I’ll just resize them to be 6.5.cm and run them and them in ar10…


I think I’ve got buy-itis so I got to see a doctor for that

 

[Kocher]

Comparing pressures in bolt vrs has gun with the 6ARC should yield sim. Results in the Dasher compared to the 6GT..


2,550 fps w/ 105 pill @ 52,000 cup
2,850 FPS w/105 pill @62,000 cup

This comparing a bolt /gas in 6ARC….
300 fps differance when using a double base spherical powder

Varget shows

2,400 @ 52,000 cup
2,750 @ 62,000 cup pressure

it does better with a larger case in the BR and GT cases?

Is this the same results guys are getting when shooting the GT versus the Dasher??
Is the difference about 250 or 300 FPS?

Or do you guys over pressure the six Dasher and bring it up to the 62,000 psi?
I’m just spitball in here..