Gordon's Reloading Tool

[Beiruty]

Caution. My understanding is using the gas hole over compensates because it assumes the hole vents to the outside vs to a small tube.

I tried using it with my AR and got 'wonky' results.
All my other results have been without a 'gas hole' in the barrel.

I would suggest to Gordon to use 2-chamber designs for his simulator before and after the gas hole instead of gas-leak approach which could be valid for Revolver's chamber.

 

[jelenko]

I would suggest to Gordon to use 2-chamber designs for his simulator before and after the gas hole instead of gas-leak approach which could be valid for Revolver's chamber.

There's a forum on Discord for discussion about GRT. You could make the suggestion there.

 

[dstoenner]

I have been using GRT for over a year now. I have found it good on giving me a chamber pressure with a load if I back annotate the first and second powder variables.

But when I set up my AR15 the curves were in the over pressure for what I had shot in my AR15 XTC matches for years. Based on that I should have been losing all of my brass in one firing but I would typically get 7 reloads out of LC brass. I just knew something was a miss here but not what it was.

Now with the discussion of the modeling of the gas port hole here got me thinking. I have an experiment I can run. I had just got 200 new Lapua cases and did all my brass prep and loaded them up to do fire forming. 100 for the AR15 and 100 for my 700 Bolt 223. I shot 50 last weekend in my AR15 and measured the velocity. When I plugged it into GRT a load of 24.0 IMR4166 with a 68gn Hornady HPBT, it was in the 95 percentile of pressure. That is not a hot load but GRT sure thinks it is.

I will shot 50 in my 700 on the 18th and get a velocity for it. Then plug it into GRT, get the powder variables and back annotate them into the AR and then start adjusting the gas port hole till I get back to the AR15 velocity and see what that does for the pressure.

My thought is that the simulation bleeds off to much pressure and that causes it to create higher pressure curves to compensate.

If somebody has another test lets put our heads together.

David

 

[Beiruty]

I have been using GRT for over a year now. I have found it good on giving me a chamber pressure with a load if I back annotate the first and second powder variables.

But when I set up my AR15 the curves were in the over pressure for what I had shot in my AR15 XTC matches for years. Based on that I should have been losing all of my brass in one firing but I would typically get 7 reloads out of LC brass. I just knew something was a miss here but not what it was.

Now with the discussion of the modeling of the gas port hole here got me thinking. I have an experiment I can run. I had just got 200 new Lapua cases and did all my brass prep and loaded them up to do fire forming. 100 for the AR15 and 100 for my 700 Bolt 223. I shot 50 last weekend in my AR15 and measured the velocity. When I plugged it into GRT a load of 24.0 IMR4166 with a 68gn Hornady HPBT, it was in the 95 percentile of pressure. That is not a hot load but GRT sure thinks it is.

I will shot 50 in my 700 on the 18th and get a velocity for it. Then plug it into GRT, get the powder variables and back annotate them into the AR and then start adjusting the gas port hole till I get back to the AR15 velocity and see what that does for the pressure.

My thought is that the simulation bleeds off to much pressure and that causes it to create higher pressure curves to compensate.

If somebody has another test lets put our heads together.

David

The bleed off the gas is after the bullet passes the gas hole. You are on the right track.
You can tune the powder model in a bolt rifle, save the parameters as new tuned powder.
Then, For your AR load, you can set the gas hole at the correct distance and adjust the hole size until the predicted MV matches the observed MV.

 

[jelenko]

I have been using GRT for over a year now. I have found it good on giving me a chamber pressure with a load if I back annotate the first and second powder variables.

But when I set up my AR15 the curves were in the over pressure for what I had shot in my AR15 XTC matches for years. Based on that I should have been losing all of my brass in one firing but I would typically get 7 reloads out of LC brass. I just knew something was a miss here but not what it was.

Now with the discussion of the modeling of the gas port hole here got me thinking. I have an experiment I can run. I had just got 200 new Lapua cases and did all my brass prep and loaded them up to do fire forming. 100 for the AR15 and 100 for my 700 Bolt 223. I shot 50 last weekend in my AR15 and measured the velocity. When I plugged it into GRT a load of 24.0 IMR4166 with a 68gn Hornady HPBT, it was in the 95 percentile of pressure. That is not a hot load but GRT sure thinks it is.

I will shot 50 in my 700 on the 18th and get a velocity for it. Then plug it into GRT, get the powder variables and back annotate them into the AR and then start adjusting the gas port hole till I get back to the AR15 velocity and see what that does for the pressure.

My thought is that the simulation bleeds off to much pressure and that causes it to create higher pressure curves to compensate.

If somebody has another test lets put our heads together.

David

David - When I use 24 gr of 4166 in a Wylde chamber with 31.2 gr of fired case volume and an H68 at 2.250, I get max pressure of 45.8K - right at the 75% level. I'm thinking there's a data input error somewhere.

 

[dstoenner]

David - When I use 24 gr of 4166 in a Wylde chamber with 31.2 gr of fired case volume and an H68 at 2.250, I get max pressure of 45.8K - right at the 75% level. I'm thinking there's a data input error somewhere.

That is what i sort of thought but I’ll check again. The only difference in my bolt and AR is barrel length and the gas port

 

[dstoenner]

I did go back and check things and could find nothing out of place. I went to check the vent hole and a new warning page came uip that said that this was meant for muzzle break or the like that are created within the barrel itself. They are not meant for gas ports to support cycling actions.

So it looks like they do not support AR15 directly and that we have to be creative to bend the tool to meet our needs.

 

[jelenko]

I did go back and check things and could find nothing out of place. I went to check the vent hole and a new warning page came uip that said that this was meant for muzzle break or the like that are created within the barrel itself. They are not meant for gas ports to support cycling actions.

So it looks like they do not support AR15 directly and that we have to be creative to bend the tool to meet our needs.

David - I got the same feedback when I asked the question on their forum.

If you send me your grt load file, I can take a look to see if I can find why's it's showing high pressure.

 

[dstoenner]

Check out my new thread for my results on the experiment I proposed about the gas port hole of an AR15 within the scope of these tools

GRTools and modeling an AR15

In the thread Gordon's Reloading Tool https://forum.accurateshooter.com/threads/gordons-reloading-tool.4029708/ starting at post 23, I brought how GRTools seemed to do a bad job of modeling and predicting pressure and velocity. Seemed like every load I tried was over pressure. @jelenko...

forum.accurateshooter.com

David

 

[SeabeeKen]

Gordon may have already worked that out. I know it has come up before with him