How do you temperature tolerance test?

[Keith Glasscock]

I've tried a couple of times to test the temperature tolerance of RE-15 in my dasher. I just got a wake up call that my testing and resultant loading practices were incorrect.

So, how do you test? How do you determine what load you should pre-load?

All of this is based on f-class where we must pre-load and using a temperature sensitive powder.

I know that there are more stable powders, but even Varget changes with temperature.

 

[pcrowe]

I've tried a couple of times to test the temperature tolerance of RE-15 in my dasher. I just got a wake up call that my testing and resultant loading practices were incorrect.

So, how do you test? How do you determine what load you should pre-load?

All of this is based on f-class where we must pre-load and using a temperature sensitive powder.

I know that there are more stable powders, but even Varget changes with temperature.

I basically don't decide on loads used in the summer until I can test them in at least close to the right temps.

 

[Keith Glasscock]

The effect of temperature on powder burn rate is not solely limited to the temperature of the loaded round. A significant amount of powder burns in the barrel, which will heat up significantly during the course of an F-Class string of fire. For that reason, I don't believe heating/cooling just the loaded round itself will fully mimic the effect of a significantly different ambient temperature combined with heating of the chamber/barrel.

I agree, but I've never chrono'd during a string. As I come to the end of life of some barrels here, I'll have to add that test to the barrel's "bucket" list.

I have a 284 barrel that is long in the tooth and I'm trying all kinds of silly stuff with it.

 

[jlow]

When I was at the Brian Litz class in February, h

I would also be interested to hear if someone has a reliable method to do this. The effect of temperature on powder burn rate is not solely limited to the temperature of the loaded round. A significant amount of powder burns in the barrel, which will heat up significantly during the course of an F-Class string of fire. For that reason, I don't believe heating/cooling just the loaded round itself will fully mimic the effect of a significantly different ambient temperature combined with heating of the chamber/barrel.

QuickLoad has a temperature setting button that appears when the "write" feature is enabled, such as when adjusting a powder burn rate. I have played around with adjusting the temperature in the program recently, but have not had the opportunity to actually determine velocity at significantly different ambient temperatures over longer strings (15+) of fire and see how close the predictions in QL come to reality. If the QL temp feature proves to be fairly reliable, it would be incredibly easy to use it to make minor adjustments to a load based on predicted temperatures. Otherwise, I don't know of a good way to do this other than simply testing velocity over long strings of fire at a variety of different temperatures.

As far as I have found, QL's temperature feature does not work.

 

[Ned Ludd]

I agree. I don't typically do that either because it's a PITA and seems like a lot of extra rounds down the barrel. However, I am looking forward to trying it at least once or twice for the reasons you mentioned and to see how the reliably QL temperature feature works. The only problem with that is that the temperature in San Diego is usually pretty steady at this time of the year. I'd like to do the test on two days where the ambient temperature differed by at least 20 degrees.

 

[Ned Ludd]

When I was at the Brian Litz class in February, h

As far as I have found, QL's temperature feature does not work.

Can you expand on that a bit? The feature certainly "works", that is to say that when you change the temperature value, pressure and velocity also change as you'd expect. However, from playing with the feature in silica, it seems to me that the changes in velocity/pressure it predicts for a given temp differential are larger than I would have expected. Is that what you're indicating?

 

[ireload2]

Does the ideal gas law tell you anything of value?

 

[Hosted]

I'll be watching this as well. I was just getting ready to load up quite a few 223 rounds tonight and try to compare some different powders in the next week. I'm running out of Varget and keep missing it when it is in stock so I want to compare some other powders like RL15 to see what my actual results are. We are going to have a 40-50 degree swing in the next week so I was just planning on shooting different powder charges through the chrono at 100 and then comparing everything at 500 yards also. I would like to hear if there is a more correct way to do it.

 

[jlow]

Can you expand on that a bit? The feature certainly "works", that is to say that when you change the temperature value, pressure and velocity also change as you'd expect. However, from playing with the feature in silica, it seems to me that the changes in velocity/pressure it predicts for a given temp differential are larger than I would have expected. Is that what you're indicating?

That is exactly what I mean.

 

[mac86951]

I do a load work-up first. Then another at height of summer on calm day with ammo in sun for 1 hour (egg cooking temp locally)

I've heard of others timing round in hot chamber to accomplish same effect.

Same in winter without sun (if you have one during that season).

Without imperical testing I doubt you'll capture the lot to lot variations that are possible. Calculations are only as good as the formula applied.

With 223 I have a 0.3gr variation between seasons. I tested and adjusted for velocity and checked for appropriate accuracy. My accuracy loads are rarely at a pressure that local temperature variations cause overpressure signs FYI.


-Mac

 

[Mozella]

I try to take a reasonable approach for these sorts of variables. I typically load F-Class ammo the week before a weekend match. I take a look at the forecast temperature for the morning of the match and plug that data into QL. Then I fiddle with the charge weight in an attempt to make the predicted MV match the predicted MV of my "standard" load.

I have given up on trying to make the QL predicted MV match my ACTUAL MV, but I figure that making a small increase or decrease in my normal charge weight based on how QL thinks temperature changes muzzle velocity is more likely to help rather than hurt.

Then I load all 70 rounds the same. I suppose I could make an "early morning" batch and a "late morning" version, but I don't.

At the match I try to keep my ammo box in the shade and I avoid letting a round sit in a hot chamber any longer than necessary.

I don't know if any of this works or not. It's not ideal, but it's not difficult either and I feel better having made some sort of effort to go in what I hope is the right direction.

 

[jlow]

I try to take a reasonable approach for these sorts of variables. I typically load F-Class ammo the week before a weekend match. I take a look at the forecast temperature for the morning of the match and plug that data into QL. Then I fiddle with the charge weight in an attempt to make the predicted MV match the predicted MV of my "standard" load.

I have given up on trying to make the QL predicted MV match my ACTUAL MV, but I figure that making a small increase or decrease in my normal charge weight based on how QL thinks temperature changes muzzle velocity is more likely to help rather than hurt.

Then I load all 70 rounds the same. I suppose I could make an "early morning" batch and a "late morning" version, but I don't.

At the match I try to keep my ammo box in the shade and I avoid letting a round sit in a hot chamber any longer than necessary.

I don't know if any of this works or not. It's not ideal, but it's not difficult either and I feel better having made some sort of effort to go in what I hope is the right direction.

In my experience, you can in fact have QL match your MV but only for the specific temperature you chrono the rounds in and adjust QL with. Once the temperature change significantly, the predicted MVs using QL will change in an exaggerated fashion than your actual MV.

 

[Ned Ludd]

jlow, that is what I inferred from your previous comments. I think the question that still remains is whether the change predicted by QL is proportional to the actual change. In other words, if QL predicts you need to drop the charge weight by 0.2 gr for every 10 degrees increase in ambient temp to keep the velocity the same, but by empirical testing you determine that it's only 0.1 gr for every 10 degree change, as long as that value remained constant within the temp range you normally shoot, it would still be an effective way to adjust your load based on generalized weather forecasts. I'm not expecting QL to be the end-all, be-all. However, if it can be used to predict I need to drop the charge weight I use on a 75 degree day by some amount to get it pretty close in terms of velocity for a 90+ degree day, I'd be completely happy with that.

It seems as though the only way to know the answer is to do enough testing at different ambient temperatures that you can assess whether the QL predictions are at least proportional to the actual values, even if they're not accurate. To be honest, I haven't messed around enough with QL to know the answer to this, but it also seems as though it should be possible to overwrite the temperature sensitivity value in the program for a specific powder and save the file. My understanding is that those values were obtained from the manufacturer, but I don't know if they can be altered and saved like we can do with burn rate factors. If they can, it's a simple matter of adjusting the value to match your actual temperature-velocity data.

 

[jlow]

jlow, that is what I inferred from your previous comments. I think the question that still remains is whether the change predicted by QL is proportional to the actual change. In other words, if QL predicts you need to drop the charge weight by 0.2 gr for every 10 degrees increase in ambient temp to keep the velocity the same, but by empirical testing you determine that it's only 0.1 gr for every 10 degree change, as long as that value remained constant within the temp range you normally shoot, it would still be an effective way to adjust your load based on generalized weather forecasts. I'm not expecting QL to be the end-all, be-all. However, if it can be used to predict I need to drop the charge weight I use on a 75 degree day by some amount to get it pretty close in terms of velocity for a 90+ degree day, I'd be completely happy with that.

It seems as though the only way to know the answer is to do enough testing at different ambient temperatures that you can assess whether the QL predictions are at least proportional to the actual values, even if they're not accurate. To be honest, I haven't messed around enough with QL to know the answer to this, but it also seems as though it should be possible to overwrite the temperature sensitivity value in the program for a specific powder and save the file. My understanding is that those values were obtained from the manufacturer, but I don't know if they can be altered and saved like we can do with burn rate factors. If they can, it's a simple matter of adjusting the value to match your actual temperature-velocity data.

Gstaylorg – that’s an interesting perspective. Frankly I have also not tested it that way either as I pretty much stopped when the extrapolated MV was nowhere close to what I was seeing. Agree that it’s going to take some experimenting to figure out how this turns out.

 

[mysticplayer]

Living in Canada, I see the full range of temps and it can drive you to drink when swings make a great load... stink. The wildest swing was testing in a warm spring around 25C and then walking onto the line at Ben Avery and it was a balmy 40C.

Yeah, that was a frustrating week.... choo choo.. BAM

So now I test all year.... Change your powder step 1... Varget varies but a whole lot less then Re 15. Or try AR Comp which is supposed to be the temp stable variant of Re15???

Then find out where the RIFLE changes for the temp range you will likely see. It is really rare to see a swing of more then 15C (roughly 40F) in a match weekend so test on each side of the most likely temp range you will compete in.

Note that I said RIFLE change and I do mean that... stocks, barrels, actions and even scopes can change over large changes in ambient temps. How much? Does it matter? Find out.

And then see how this affects your load tuning to keep at the performance you are after. I like to shoot a rifle over a couple of years before I figure out it is dialed in.

Jerry

 

[Mozella]

In my experience, you can in fact have QL match your MV but only for the specific temperature you chrono the rounds in and adjust QL with. Once the temperature change significantly, the predicted MVs using QL will change in an exaggerated fashion than your actual MV.

You're quite correct. It's easy enough to match a QL predicted MV with a real world example by fiddling around with the powder Burning Rate Factor (Ba). But only at a single point. If you then ask QL to produce a matrix of predicted MV vs charge weight, as you might do during load development testing, you will find that the calculated MV values diverge from measured performance significantly. The same goes for temperature variations, as you point out. You are correct when you say the further you get from the temperature at which you match the prediction to your measured MV, the worse the QL prediction gets.

That being the case, I no longer try to fine tune a recipe so that QL matches one of my measured data points, much less a range of carefully measured "real world" data points. But I do use QL as a guide on how much I should increase or decrease the charge weight of my "standard" competition ammo recipe if I'm reloading with the anticipation of shooting at higher or lower temperatures. I know this isn't scientifically perfect, but I think it's a reasonable approach and I'm sure it's better than my wild guess.

 

[techshooter]

I take a consumer medical type heating pad to the range and wrap 10 rounds in it for 20 minutes or so until they reach temperature. They get to about 120F in my pad when it is 45 degrees out. I then shoot 10 "cold" rounds through the rifle to get the barrel warm/hot, measuring the MV for all shots. At this point, I shoot the 10 hot soaked rounds and see what the MV does. If you have previously calibrated QL to the cold rounds, you can see what incremental charge weight increase it will take to get QL to match the "hot" rounds. I look at the resulting predicted pressure for the hot case, and if it is still safe, and the rifle is still shooting, I'm good to go. I will typically see about a 25-30 FPS delta for the 45 degree to 120 degree test with my 6 Dasher running 33 grains RL-15 under a 105 Berger VLD. As I tune my load to be on the slow edge of the node when cold, this lets the rifle shoot under all temperature conditions, as the 25 FPS delta is not enough to take it out of the OBT zone.

Chris Long