Temperature Sensitivity of 8 Powders for .223 High Power Service Rifle

[BillC79]

I am in the process of identifying some substitute/replacement powders for Varget and IMR 8208 that I use in XTC high power matches with a .223 service rifle and with practice ammunition. A first step for me was evaluating temperature sensitivity of the powders. I have attached the data panels and graphs for tests run with 77 grain Sierra MatchKing and 55 grain FMJ-BT bullets that may be of general interest.
These are included in a draft of a review on my website which has more information on the methods used and conclusions.
A draft for review is at:
https://www.wlcastleman.com/equip/shoot/t223/index.htm

Comments and suggestions for improvement are appreciated.
Thanks for looking.

Update: 8/19/2021 - It is now nine powders (see review link above)

 

[mike mccormick]

Interesting data. Thank you! It would be interesting to see how group size correlates with the temperature changes.

 

[flyingbrass]

Thanks for posting this. I'm also interested in temperature stable powders for .223. A buddy and I here in Arizona have both been using 8208 XBR with excellent results with Hornady 73 ELD and Sierra 77 TMK. These days powder availability can be a problem, and it would be great to have some alternatives. From your data so far, both IMR 4166 and AR Comp appear to be good candidates for our 40F to 115F temperature range.

In researching powder temperature stability online over the years I've seen quite a bit of contradictory information. It seems that stability varies somewhat by the particular cartridge and load used, which is what your results so far are showing in .223. Charts ranking powders by general temperature sensitivity are likely misleading because what may be relatively stable with one combination may not be in another.

It is interesting that AR Comp velocities decreased with temperature increase. In handgun powders, WSF does the same, at least with mild to medium 9mm loads.

 

[RegionRat]

A suggestion would be just a few words on how you arranged the testing in terms of temps and experimental set up?
Just the ammo, or the whole rig plus the ammo?

 

[BillC79]

A suggestion would be just a few words on how you arranged the testing in terms of temps and experimental set up?
Just the ammo, or the whole rig plus the ammo?

Thank you for your suggestion. The website review has an entire description of the methods and setup used that is difficult to include in this forum succinctly. The link to the methods section is below:

Methods

 

[Stumpy1]

Very nicely done, Bill. Thanks for posting your work!

Frank

 

[Jon D]

The work you have done is great. The powders we have/had available to us are simply amazing! Have you taken a look at a ballistic program to see what it actual means? Using the numbers you provide for N140, because it was one of the more temp sensitive powders listed there is about 1 moa vertical change at 600 yards using the 77 due to the velocity difference for 34 vs 100 degree. If you sight in at 65 degrees there is only a 1/2 moa change up or down from 34 to 100 degrees. That is still within the x-ring. If you really get technical, air density changes, humidity, bullet ballistic coefficient variation, and standard deviation of the velocity, create enough noise that the actual on target representation of velocity variation due to temperature change gets lost in the data, when using a somewhat temp stable powder. Going to a more aerodynamic bullet at 600 will reduce all of this variation even more. If supplies are running low, I would shoot any of the powders listed for 77gr bullet and be happy. None of them are going to put your first shot out of the ten ring due to velocity difference alone. If you can't find an extreme temp stable powder, I'd still try to find an extruded powder and for that first shot, add a click if it's cold, take one off when it's hot. Pretty simple. If you have to shoot standard ball powder like 748 or blc2, then you have a little more thinking to do.

 

[SVT_Tactical]

Great post with excellent data and will be helpful to lots of folks looking for substitute powder given the rarity of varget and other more desired powders.

 

[BillC79]

.... Have you taken a look at a ballistic program to see what it actual means? ......

Thanks for your very helpful comment!
As I am putting this data together, there is a danger of momentarily getting lost in the trees when I really want to understand the forest. I’ll add at least one table to the website review with data from a ballistic program indicating differences in predicted point of impact at 300 yards for 77 grain bullets at temperature extremes for each powder. Most shooters I know are using bullets heavier than 77 grains with service rifles at 600 yards.

 

[Oso]

Bill,

I really appreciate the science project... the graphs are great!

Although different powders, I know most people treat AR Comp and H4895 more or less as the same... same charge weights come within a couple of fps of each other with similar temperature insensitivity. I noticed that you tested AR Comp for the 77gr and then used H4895 for the 55gr. Was this the reason or simply a matter of what you had on hand at the time?

Thanks

 

[BillC79]

............Although different powders, I know most people treat AR Comp and H4895 more or less as the same... same charge weights come within a couple of fps of each other with similar temperature insensitivity. I noticed that you tested AR Comp for the 77gr and then used H4895 for the 55gr. Was this the reason or simply a matter of what you had on hand at the time? ..........

I only tested H4895 because I was looking for more easily obtainable powder than IMR 8208 XBR to use in 55 grain practice ammunition and had an underutilized supply on hand since I historically have only loaded ammunition with it for my Garand. H4895 performed much better with 55 grain bullets than I had expected it would. In retrospect, it would have been useful to look at its performance with 77 grain bullets.

 

[Cfshooter]

Great info, thanks for sharing!

 

[lotech]

I haven't tried all powders, but for AR 5.56 / .223 loads using bullets in the 65 - 75 ( heaviest I've tried) grain weight range I've not found a better powder from an accuracy perspective than H4895. It doesn't flow through a measure as well as some powders. For many other rifle cartridges from 6mm Remington through .300 magnums, Hodgdon Extreme powders (H4895, H4350, and H4831) work best for my needs.

 

[RegionRat]

Thank you for your suggestion. The website review has an entire description of the methods and setup used that is difficult to include in this forum succinctly. The link to the methods section is below:

Methods

Thanks for the reply, I didn't catch the site navigation links on the first look but I noodled around this time.
Loved the photography sections with the ones from 395 being favorites.

 

[Jon D]

Konrad Powers recently posted a video about powder measure variation and on target results for high-power. It's not the same thing you are looking into, but similar enough that you might get some ideas Might want to give it a watch.

 

[Ned Ludd]

Bill - very interesting results, thanks for posting!

One thing I am curious about is your temperature measurements. From your reference: "Tests were run at cartridge-powder temperatures from 34°F to 102°F (1 to 39°C) which cover temperatures that I encounter at matches in North and Central Florida and are technically feasible to run with my available resources."

Does this mean the ambient temps, or did you have some way such as a thermocouple or temperature probe to actually measure the powder temp? I can't really tell from the description. Tests of this nature are typically performed at ambient temps, or sometimes by heating/cooling the loaded cartridges. However, one must be cautious with interpreting such results. A substantial proportion of the powder will burn within the first 8-10" of barrel (i.e. outside the case). Because of that, if the barrel is allowed to warm up at all as compared to ambient temperature, the resultant velocity will be affected to a certain degree by the barrel temperature because that is where a significant proportion of the chemical reaction is taking place. This is not a deal-breaker; it just means that its important to let the barrel return to ambient temperature between shots if that's how the experiments were conducted.

 

[RegionRat]

Here you go @Ned Ludd

https://www.wlcastleman.com/equip/shoot/t223/methods.htm

He answered my post with that link to the experimental method and procedures write up. I missed the site navigation links on his page on the first look and asked the same questions.

 

[Ned Ludd]

Thanks RegionRat- I also missed that. It seems Bill was about as careful as you can be to keep temperature fluctuation to an absolute minimum. Nonetheless, 5 shots in a short time period is certainly enough to warm the barrel above ambient, and it is simply not possible to chamber a round and fire it fast enough that some warming does not occur. I have seen similar tests where a thermocouple was placed inside a powder charge to determine how quickly the powder inside a chilled round would warm up in the chamber of a rifle at ambient temperature. Full warming was not instantaneous, but within seconds some measurable warming had nonetheless occurred. For that reason, my feeling has always been that doing these types of tests when the ambient temperature, and therefore the temperature of the rifle/barrel, as well as the loaded ammunition, were cold/medium/hot is the best approach. Unfortunately, that makes the experiment much more difficult and time-consuming, and I doubt it would change the end results. The most shocking results of these tests to me were that the velocities with IMR4166 and AR Comp stayed the same, or even decreased as the temperature went up. I would not have expected that with either of those powders.

 

[RegionRat]

When you watch airborne machine guns tested in altitude (Arctic) conditions, there is always some change in the trajectory from cold to the end of the first belt. Even with the best powders. All to be expected.

Those were all good powders for the purpose of his testing and there were no surprises.

 

[BillC79]

... Nonetheless, 5 shots in a short time period is certainly enough to warm the barrel above ambient, and it is simply not possible to chamber a round and fire it fast enough that some warming does not occur. I have seen similar tests where a thermocouple was placed inside a powder charge to determine how quickly the powder inside a chilled round would warm up in the chamber of a rifle at ambient temperature. Full warming was not instantaneous, but within seconds some measurable warming had nonetheless occurred. For that reason, my feeling has always been that doing these types of tests when the ambient temperature, and therefore the temperature of the rifle/barrel, as well as the loaded ammunition, were cold/medium/hot is the best approach. Unfortunately, that makes the experiment much more difficult and time-consuming, and I doubt it would change the end results. The most shocking results of these tests to me were that the velocities with IMR4166 and AR Comp stayed the same, or even decreased as the temperature went up. I would not have expected that with either of those powders.

I’ll respond on two points:
1) Rifle chamber temperature and powder temperature at time of combustion.
I agree that rifle chamber temperature increases probably increase cartridge powder temperature under some match conditions.
I don’t believe the effect is occurring to a significant extent under the rapid-fire conditions of my study. I recorded the mean and standard deviation of the two sequential 5-shot strings for each powder. If you look at the means from 34°F tests which were run first when both the cartridges and the barrel chamber were coolest, the second test mean velocity was lower than the first test mean velocity in 6 out of 9 tests.

See raw data with test means and standard deviations at:

https://www.wlcastleman.com/equip/shoot/t223/34raw.jpg

A more important chamber warming effect on cartridge powder may occur in slow fire conditions of a 20 shot string. As the cartridge at lower ambient temperature is loaded single shot into the heated chamber in the middle of the string, there is probably enough time while the shooter aims in prone position and fires for the cartridge to significantly heat. This may be the part of the shooting process where temperature insensitivity of the powder is most important.

2) AR-Comp (Eurenco Bofors PR34TZ) temperature response
AR-Comp appears to contain an inhibitor of combustion/pressure that decreases velocity with increasing temperature along much of its temperature:velocity relationship. This is discussed and documented in the full website review. IMR 4166 may have a similar functioning inhibitor.