GRT / QL question(s)

[itchyTF]

Haven't played around with this much and lately haven't been pulling the trigger much either. But I thought I'd take my last load workups with a 6.5 Creed (105gr BK) in an AR10 (DPMS, 24" +2 barrel with SA adj gas block) and see what GRT has to say. Velocities weren't even close to what GRT says they should be.
It looks like people tweak Ba, k & Start Pressure to match results with the prediction. Each one has an effect so how do you determine which one(s) to adjust?
@222Jim says, in another thread, that these simulation programs really aren't intended for gassers. I suppose this is due to the gas losses that aren't present in bolt guns.
So, what to do? Tweak variables so that results match prediction or don't use the software for gassers? If usable, what variables and in what order?

 

[J_idaho]

Use the obt button

 

[itchyTF]

I was planning on using that but was wondering if the velocity predictions weren't close would the OBT info be correct?

 

[jelenko]

You need to first enter the measured capacity of your fired cases, the length of the bullet you're issuing and the coal.
Then fire 7 to 10 shots across a chrono and record their muzzle velocities on the measurements tab.
Then run the obt function - out will automatically calibrate the powder to your specific rifle and load.

 

[Chestnut]

The more variables you can measure an input the more accurate the program will be.

In addition to capacity, barrel length (duh?) and trimmed case length have helped me dial.

Some powders are more accurate than others. with H335 and A2230 I've had really good luck getting close loads on an AR15 and AR10 using OBT iteration. If you haven't read https://forum.accurateshooter.com/t...lets-with-gordons-reloading-tool-grt.4113273/ it's been helpful. Also https://forum.accurateshooter.com/threads/2-words-of-caution-in-how-to-use-grt.4151990/

 

[SeabeeKen]

Haven't played around with this much and lately haven't been pulling the trigger much either. But I thought I'd take my last load workups with a 6.5 Creed (105gr BK) in an AR10 (DPMS, 24" +2 barrel with SA adj gas block) and see what GRT has to say. Velocities weren't even close to what GRT says they should be.
It looks like people tweak Ba, k & Start Pressure to match results with the prediction. Each one has an effect so how do you determine which one(s) to adjust?
@222Jim says, in another thread, that these simulation programs really aren't intended for gassers. I suppose this is due to the gas losses that aren't present in bolt guns.
So, what to do? Tweak variables so that results match prediction or don't use the software for gassers? If usable, what variables and in what order?

Grt is also for gas guns. There is an option to add the location and size of the gas port in the settings.

 

[jelenko]

Grt is also for gas guns. There is an option to add the location and size of the gas port in the settings.

I use GRT for my ar 'spacegun'.
From the Discord discussion group, I learned that we should not use 'Gas leakage' parameter. I tried using it, but results were way off.

I should mention that for my ar spacegun, with all the measurements from my brass, load and velocities, I've found 'nodes' either at the predicated powder charge or within +/- .2grains.
But please note - I test prone with a sling - if I get several groups 1/2 MOA +/- I call it a node.

 

[itchyTF]

Is the location and size of the gas port the same as the gas leakage parameter?

 

[jelenko]

Is the location and size of the gas port the same as the gas leakage parameter?

According to the expert on GRT's discord server, no.
The recommendation was to not try to simulate the gas port.
See my post above.

 

[SeabeeKen]

According to the expert on GRT's discord server, no.
The recommendation was to not try to simulate the gas port.
See my post above.

gas leakage is when gases are leaked to the atmosphere such as a revolver cylinder gap or direct impingement. I have the port for my AR and gap for my Ruger Redhawk and it seems to work fine for me. I haven't used it for my M-1A since I havent got around to setting it up yet

 

[SeabeeKen]

Is the location and size of the gas port the same as the gas leakage parameter?

Gas leakage is where the port is set up and it will show up on the graph

 

[SeabeeKen]

Is the location and size of the gas port the same as the gas leakage parameter?

I recommend you get on the Discord as Charlie is the most knowledgeable person I know with using the software.

 

[jelenko]

I recommend you get on the Discord as Charlie is the most knowledgeable person I know with using the software.

Just to add, he is very knowledgeable.

 

[itchyTF]

I recommend you get on the Discord as Charlie is the most knowledgeable person I know with using the software.

I consider myself reasonably computer literate but for some reason I find Discord difficult to navigate. I joined in 2020 but have used it very little. I don't know how to find Charlie or GRT or anything else on that site.
Apparently I'm "part of / attached to / member of" MEE6 in Reloading. Don't remember how I got there and have never used or browsed it. Maybe my problem is I don't do Facebook, twitter, X, or any of the other social sites.

 

[itchyTF]

I recommend you get on the Discord as Charlie is the most knowledgeable person I know with using the software.

I'm on Discord. How do I find GRT and/or Charlie? I did a search for GRT and Gordon't reloading tool under Discover Servers and nothing popped up.

 

[SeabeeKen]

I'm on Discord. How do I find GRT and/or Charlie? I did a search for GRT and Gordon't reloading tool under Discover Servers and nothing popped up.

Its there. I was on it last night

 

[itchyTF]

I must need to do something different but I don’t know what. Do I need to have a certain status or have my own server or …..?

 

[jelenko]

I must need to do something different but I don’t know what. Do I need to have a certain status or have my own server or …..?

You shouldn't. Once you log into Discord [you do need to set up an account so you can log in],

Here's the link from my browser looking at GordonsReloading

 

[itchyTF]

Tried clicking on GordonsReloading but nothing happened. Doesn’t appear to be a live link.

 

[jelenko]

Tried clicking on GordonsReloading but nothing happened. Doesn’t appear to be a live link.

Uh oh. Something going on with your browser. The link takes me to the GordonsReloading server on Discord.

At worst you should be getting a login page or some error page because you're trying to access a page you don't have permissions for.

ETA: Just a thought, try right clicking on the link, then click on 'open in a new tab'.