Range Report Methods for modeling temp variation for powders?

[mattmcg]

Recently I have been playing around with the ballistics program Shooter for the Android OS (a very nice program BTW) and was thinking about how I should go about modeling muzzle velocity variations with powder at different temperatures in specific guns. Being a bit of a math-hound, I was thinking about how I might model it to find a linear or curvi-linear regression equation to build a predictive model to better understand velocity variations and then subsequently use that info in the Shooter app.

Yeah, I realize that most think this is a bit of a wasted exercise and that I should simply, "get out and shoot" but frankly with the economy on the fritz and an extended bout of unemployment, I've got the time to hone my ballistics calculations (and shoot all I can these days already)..... So I'm up to the task. Plus I'd like to see if temp variation matters at all or if it is simply something in the noise of shooting. I realize that temp sensitivity is powder specific so for reference, I use Varget, H4831SC, H4350, H322, and H4895 in various loads. All powders in the Hodgdon's Extreme line.

My first question is, are there any good general references or tools available that have tested and modeled specific powders? I see that Quickload doesn't provide anything although I think this would be an excellent addition to their program.

My second question is how should one go about prepping certain temp scenarios to acquire sample data? Can I do it in one shot or do most just chrono over a longer period of time in different temps and simply plug in the single sample to improve the insight?

I'm sure I'm barely scratching the surface on this topic so I'm curious what others have done.

 

[Lindy]

Re: Methods for modeling temp variation for powders?

It's not a waste of time. At or beyond 700 yards, the muzzle velocity variation with temperature can be quite significant.

Some manufacturers publish data about the temperature sensitivity of their powders.

With many modern powders, I find 1 fps per degree F. works pretty well. But I chronograph mine at different temperatures.

You might find this paper interesting:

http://www.shootingsoftware.com/ftp/Pressure%20Factors.pdf

Denton wrote a subsequent article to that one, which used to be available on this site, but appears not to be now.

Also see this thread:

http://www.snipershide.com/forum/ubbthreads.php?ubb=showflat&Number=1238626

 

[Rafael]

Re: Methods for modeling temp variation for powders?

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: mattmcg</div><div class="ubbcode-body">
My first question is, are there any good general references or tools available that have tested and modeled specific powders? I see that Quickload doesn't provide anything although I think this would be an excellent addition to their program.
</div></div>

Quickload does allow for temp variation.

In the "Charge" window, click the square icon at the upper left corner of the window.
This will allow editing of powder properties.
When this is enabled, you will see a new square icon at the lower left of the same window that will allow powder temp alteration. You can enter different temps and note the predicted variation over a range. It is not as good as field testing but it is a start.

Of course when Lindy gives an opinion, as he did above, I try to follow him and I almost always learn something. When I don't learn....I wonder where "I" went wrong.

 

[mattmcg]

Re: Methods for modeling temp variation for powders?

Lindy, that article is exactly what I was looking for. The subsequent thread is also very helpful. Are there common rules of thumb for Varget, H4350, and H4831SC?

Rafael, thanks for the tip. I had certainly overlooked that button in my use of Quickload and was unaware it existed! Thanks! I guess you learn something new everyday....

 

[Lindy]

Re: Methods for modeling temp variation for powders?

Not that I know of. My Varget loads were around 0.6 fps/degree F. I have no experience with other powders.

 

[Rafael]

Re: Methods for modeling temp variation for powders?

Good to see you around, Hazardous.....errrr, Matt.
I missed the handle change and was wondering where you went.

 

[mattmcg]

Re: Methods for modeling temp variation for powders?

Yeah, after personally meeting a number of the forum members here, I was confusing people. Some referred to me as Hazardus while others knew me as Matt (as I am listed on other forums) but never as the same person. Oddly, I found myself introducing myself twice, which when you value efficiency, seemed absolutely counter productive.

I will miss one thing though. When I did badly in competition, I was named Hazardus. When I did good, Matt was the man! ;>

 

[mattmcg]

Re: Methods for modeling temp variation for powders?

So I do have some data to report back. I was playing around in Quickload looking at temp variations with their tool and found the following data for temp spreads from 30 deg to 90 deg.

24" barrelled 308Win
-Varget & Lapua 155gr Scenars varied 1.27fps/deg
-Varget & Berger 175gr LR BT varied 1.12fps/deg

26" barrelled 260AI
-H4831SC & Lapua 139gr Scenars varied 1.53fps/deg
-H4350 & JLK 130gr VLDs varied 1.33fps/deg

Interesting data. I will have to test these value with some real chrono data and refine my field dope.

 

[jbmillard]

Re: Methods for modeling temp variation for powders?

I have just measured it. Before I go to the range, I put 5-10 rounds in a sealed zip-loc bag and put them in ice water. By the time I get to the range, they're at freezing. I then quickly pull one round from the bag in ice water, throw into the action and pull the trigger -- not going for accuracy here, I just want it over the chronograph. This gives me a data point at freezing. I then shoot some rounds at ambient temperature. I'm sure it's not perfect (the gun isn't cold and it may not be exactly 32 F) but I am assuming it's close enough.

I have in the past just done a linear fit over the range of velocity. In fact, I wrote my calculators to do it for me.

As an example, my AR-10(T) with the current load gives 2800 f/s at 70 F. It gives 2750 (going from memory here) at 32 F. That gives (2800-2750)/(70 - 32) fps / deg F = 1.3 fps/deg F. Quite a bit more than I would have thought...

BallistiComp will take this single number (the 1.3) as an input.

Brad

 

[Rafael]

Re: Methods for modeling temp variation for powders?

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: mattmcg</div><div class="ubbcode-body">Yeah, after personally meeting a number of the forum members here, I was confusing people. Some referred to me as Hazardus while others knew me as Matt (as I am listed on other forums) but never as the same person. Oddly, I found myself introducing myself twice, which when you value efficiency, seemed absolutely counter productive.

I will miss one thing though. When I did badly in competition, I was named Hazardus. When I did good, Matt was the man! ;>

</div></div>
LOL
Yeah...all my real life friends call me Bob. Rafael is a play on my initials.

 

[Rafael]

Re: Methods for modeling temp variation for powders?

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: JBM</div><div class="ubbcode-body">I have just measured it. Before I go to the range, I put 5-10 rounds in a sealed zip-loc bag and put them in ice water. By the time I get to the range, they're at freezing. I then quickly pull one round from the bag in ice water, throw into the action and pull the trigger -- not going for accuracy here, I just want it over the chronograph. This gives me a data point at freezing. I then shoot some rounds at ambient temperature. I'm sure it's not perfect (the gun isn't cold and it may not be exactly 32 F) but I am assuming it's close enough.

I have in the past just done a linear fit over the range of velocity. In fact, I wrote my calculators to do it for me.

As an example, my AR-10(T) with the current load gives 2800 f/s at 70 F. It gives 2750 (going from memory here) at 32 F. That gives (2800-2750)/(70 - 32) fps / deg F = 1.3 fps/deg F. Quite a bit more than I would have thought...

BallistiComp will take this single number (the 1.3) as an input.

Brad </div></div>
What powder?

 

[jbmillard]

Re: Methods for modeling temp variation for powders?

Reloader 15. Both velocities were measured at the same time with the same chronograph.

 

[Rafael]

Re: Methods for modeling temp variation for powders?

Thanks!
Good to know.

 

[mattmcg]

Re: Methods for modeling temp variation for powders?

Hmmm, that is very interesting to see my Quickload estimates using Hodgdon's Extreme line against RL-15 and seeing the same results. I've always been under the impressing the Reloader 15 was MORE temp sensitive than any of the Extreme line.

I'm guessing that Quickload is a bit aggressive or generalized with their estimates..... Can't test this quickly enough!

Oh and JBM, thanks for the range tip on how to gain two data points quickly. Now I'm wondering how I might use the coldest and allow the cartridges to warm to grab a middle data point as well. More the ponder....