GRT 6GT help

[climbing1]

I've tried every which way to get GRT to run on my Mac with various programs, but no joy. Hopefully I'm asking the right questions giving the right inputs.

I plan on living with this cartridge for a while. I'm invested in it, have several more barrels and am not interested in making a change at least through '26. That said, I've tried both N140 and 150 and they both shoot. I'm purely curious what the modeling says is the better choice if I wanted to land on one. Aiming for 90% + fill (alpha and gap) and a 100% (or close to it) burn rate, around 2800 + - . I THINK it's going to be 150, but I'd love to see what the data says if anyone is so inclined. Sorry if I'm missing key inputs, as I haven't got to play around with it, e.g. water volume; I realize these are two different brass brands, but if you're only willing to run one, go with Alpha. Just a general idea from the model vs. real world experience with these powders.

6GT
Alpha & GAP brass
26" barrel
105 hybrids
.060 ish jump

Thank you!

 

[RegionRat]

Jump numbers are a little ambiguous. Without being in a very specific discussion with a standardized reamer, the way we communicate to internal ballistics codes is with COAL (overall length). This value affects the case fill value as well.

You will also need your internal case volume, but unless you are tuning a model with your specific velocity and such, it won't matter much because you will get a rough estimate.

Here is your basic run with your given input set at arbitrary length and for what it is worth. I put Varget in here as well. YMMV

 

[diggler1833]

N150 is the secret sweet spot for the 6GT in my opinion. I'd better get after it and buy another keg before it goes unobtanium.

Some barrels run Varget better, some do H4350 better (have one of those). N150 cuts the difference, and gives great velocity too.

I know OP wants the computer model, but it is hard to argue with the real world performance.

 

[climbing1]

Jump numbers are a little ambiguous. Without being in a very specific discussion with a standardized reamer, the way we communicate to internal ballistics codes is with COAL (overall length). This value affects the case fill value as well.

You will also need your internal case volume, but unless you are tuning a model with your specific velocity and such, it won't matter much because you will get a rough estimate.

Here is your basic run with your given input set at arbitrary length and for what it is worth. I put Varget in here as well. YMMV

View attachment 8691018
View attachment 8691021
View attachment 8691023

N150 is the secret sweet spot for the 6GT in my opinion. I'd better get after it and buy another keg before it goes unobtanium.

Some barrels run Varget better, some do H4350 better (have one of those). N150 cuts the difference, and gives great velocity too.

I know OP wants the computer model, but it is hard to argue with the real world performance.

Def appreciate everyone's replies and input. I actually have both and found a great node for both of them, but I wanted to land on one as an easy button so I don't need to think too much about it. Was hoping from an actual model that that would be informative and remove my own bias.

The node for the 150 is def lower MV, which was what I was after, so I'm thinking I'll stick with it. I'm almost at the end of life with my current barrel and have two more tee'd up, so I plan on running 6GT for a while, thus the purpose of the question around these powders. I very much hope VV won't be unobtainium! It performs awesome, low SD's and is considerably better price than Varget.

 

[diggler1833]

Def appreciate everyone's replies and input. I actually have both and found a great node for both of them, but I wanted to land on one as an easy button so I don't need to think too much about it. Was hoping from an actual model that that would be informative and remove my own bias.

The node for the 150 is def lower MV, which was what I was after, so I'm thinking I'll stick with it. I'm almost at the end of life with my current barrel and have two more tee'd up, so I plan on running 6GT for a while, thus the purpose of the question around these powders. I very much hope VV won't be unobtainium! It performs awesome, low SD's and is considerably better price than Varget.

That better price than Varget or H4350 (or anything else Hodgdon/IMR) is what is going to drive the N100 series into that unobtainable status.

I've switched from H4350 to N160 in my .260 Rem, and will probably do it again in other similar cartridges. It definitely requires a full case, and velocities are a tad lower that H4831...but for a target rifle and the fact that it is $90 cheaper/keg makes it my powder of choice. Velocity spreads with all N100 powders have been awesome for me.

Although, I did find a keg of H4350 and another keg of Varget recently that I forgot I had.

 

[4O6shootist]

Stay on top the carbon ring with N150 if you're running the upper node of 2900+, it'll get you. I ran 107smk in the ladies 6gt with N150, and it shot amazing at 2930-2940, however if I did not religiously clean every 100 rds, velocity would climb quickly and brass would show minor psi signs(ejector slot marks from tl3 bolt) primers still looked fine.

 

[climbing1]

Stay on top the carbon ring with N150 if you're running the upper node of 2900+, it'll get you. I ran 107smk in the ladies 6gt with N150, and it shot amazing at 2930-2940, however if I did not religiously clean every 100 rds, velocity would climb quickly and brass would show minor psi signs(ejector slot marks from tl3 bolt) primers still looked fine.

Thanks for the tip. I nuke the barrel every 100 and run it slower. I did notice more of a build up compared to 140.

 

[climbing1]

That better price than Varget or H4350 (or anything else Hodgdon/IMR) is what is going to drive the N100 series into that unobtainable status.

I've switched from H4350 to N160 in my .260 Rem, and will probably do it again in other similar cartridges. It definitely requires a full case, and velocities are a tad lower that H4831...but for a target rifle and the fact that it is $90 cheaper/keg makes it my powder of choice. Velocity spreads with all N100 powders have been awesome for me.

Although, I did find a keg of H4350 and another keg of Varget recently that I forgot I had.

Sounds like you're sitting on a lot of powder if you forgot those were laying around!

 

[diggler1833]

Sounds like you're sitting on a lot of powder if you forgot those were laying around!

This is one of those responses where you can't really answer truthfully.

Sometimes I go into my reloading room and it is Christmas all over again when I open up a box.