dstoenner
Silver $$ Contributor
In the thread Gordon's Reloading Tool
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 challenged that he wasn't getting high pressure with his parameters. When I was looking at his file and went to see what he put in it, low and behold a new warning message popped up saying that this parameter is basically for mussel breaks not gas ports. So I hypothesized that you could model the gas port just reduce its diameter to get the right results. I decided to run an experiment to see what the answer is. I have an AR15 match 24 inch barrel with 1:7.7 twist. I also have a 223 Remington 700 with a 26 inch 1:7 barrel. While they are not identical in all respects, I hypothesized that if I took data from the bolt gun, ran an OBT to get curve corrected values and then plugged those 2 values into my AR15 file, then adjusted the hole size till I got back to the observed velocity.
I was able to get all the data Saturday and did what I said. I took it step by step. once I plugged in the values the velocity went down below the 223 bolt gun's velocity using the trued values from the bolt gun but the pressure was still up there. My hole diameter was .3mm so I started stepping it down.. Each step the pressure went down and the velocity went up. Finally on the last step I got 2837 in a quest to match the 2850 I had gotten from this ammo on its run. The hole diameter was .1 I knew from how the steps were going that the .1 hole diameter was so small it wasn't effecting the final results. In fact the step function in the pressure curve at the gas port went away. It was now a smooth function.
My take away is that this hole modeling GRTools has is as it was intended and not for gas ports for a correct AR15 model you should just treat it as bolt gun. It fires from a locked bolt so it makes sense and the gas port does take some gas but the bullet is so far down the barrel that it doesn't make any measurable difference.
I don't like making assumptions like that but now I know I am both correct and most importantly the pressue predicted is true so if I keep it in safe territory, I and my gun are safe.
HTH to anyone else that has been perplexed by this feature that showed up recently in the tool (Or I just found it recently :-( )
David
Gordon's Reloading Tool
Not sure if anyone has posted about this yet, but this is a great open source tool for anyone that reloads. I have no experience with Quickload, but from what I have read, this appears to be a free substitute. When I entered the data for the couple of loads that I have worked up myself without...
forum.accurateshooter.com
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 challenged that he wasn't getting high pressure with his parameters. When I was looking at his file and went to see what he put in it, low and behold a new warning message popped up saying that this parameter is basically for mussel breaks not gas ports. So I hypothesized that you could model the gas port just reduce its diameter to get the right results. I decided to run an experiment to see what the answer is. I have an AR15 match 24 inch barrel with 1:7.7 twist. I also have a 223 Remington 700 with a 26 inch 1:7 barrel. While they are not identical in all respects, I hypothesized that if I took data from the bolt gun, ran an OBT to get curve corrected values and then plugged those 2 values into my AR15 file, then adjusted the hole size till I got back to the observed velocity.
I was able to get all the data Saturday and did what I said. I took it step by step. once I plugged in the values the velocity went down below the 223 bolt gun's velocity using the trued values from the bolt gun but the pressure was still up there. My hole diameter was .3mm so I started stepping it down.. Each step the pressure went down and the velocity went up. Finally on the last step I got 2837 in a quest to match the 2850 I had gotten from this ammo on its run. The hole diameter was .1 I knew from how the steps were going that the .1 hole diameter was so small it wasn't effecting the final results. In fact the step function in the pressure curve at the gas port went away. It was now a smooth function.
My take away is that this hole modeling GRTools has is as it was intended and not for gas ports for a correct AR15 model you should just treat it as bolt gun. It fires from a locked bolt so it makes sense and the gas port does take some gas but the bullet is so far down the barrel that it doesn't make any measurable difference.
I don't like making assumptions like that but now I know I am both correct and most importantly the pressue predicted is true so if I keep it in safe territory, I and my gun are safe.
HTH to anyone else that has been perplexed by this feature that showed up recently in the tool (Or I just found it recently :-( )
David
