Extreme Temp Test - 6.8 SPC, 223, x39, 6.5CM

[68wj]

It is commonly stated that ammunition performance can vary with temperature. Some powders are even sold under the claim that they are more stable. I wanted to see for myself with some of the common rounds that I shoot (factory and hand loaded).

Here's what I did:

First, thanks to Blue Bell's recall, there is room in my freezer so I loaded 5 rounds into 15 numbered magazines and left them in the freezer overnight. I then placed them in a box with a block of dry ice on top, and put that in a cooler to head to the range. I took a measurement with a digital probe inside of one of the magazines and got a reading that settled at -11.5*F. These magazines were removed one at a time and fired rapidly over a chronograph to avoid thawing the ammunition.

A frosty magazine after firing a string.


At the conclusion of each string, I reloaded the magazines with another 5 rounds. My intentions were to place the magazines in the sun to warm but some clouds moved in as I headed to the range. Instead I placed them under the hood of my vehicle and let the warm embrace of a 4.0 Jeep I6 bring them up to temperature. By the time I finished the cold ammo, I had a pile of mags under my hood. ***I do not recommend this. Ammo should be kept out of direct sun and off of engines!*** I then ran these strings over the chronograph.

Engine bay mag warmer. I took a couple readings and came up with 146.8*. Did I mention not to do this? Well, don't!


A good day at the range in my book. Seriously, you can even see my notebook in the picture.


So here it is. Enjoy.


I do want to revisit this test with a focus on AA2200 powder in the 6.8. These FMJ bullets have terrible consistency and the load represented was range fodder. My loads with Hornady HPBT and Nosler CC bullets are ~150 fps faster. I want to see if the higher pressure increases, decreases, or has no affect on the variation.

Cold brass

 

[ironworkerwill]

Now is a great time for the high heat end of the test!!!!

You have a good temp spread, WELL DONE! Im glad you had some varget to throw in too.

 

[Walkalong]

The H322 sure did well.

 

[carbine85]

Thanks for spending your time and ammo on the test. Most of this has been tested before to some extent. The normal testing is usually within a tighter temperature and the conclusion usually shows no major difference in the velocity.
When I chrono my AR10 loads I usually don't see much change in velocity with temperature change, what I do see is a change in the groups.

 

[68wj]

Thanks for spending your time and ammo on the test. Most of this has been tested before to some extent. The normal testing is usually within a tighter temperature and the conclusion usually shows no major difference in the velocity.
When I chrono my AR10 loads I usually don't see much change in velocity with temperature change, what I do see is a change in the groups.

Burning the ammo made the time worth it. Gotta love the excuse for rapid fire strings, "I just have to get the rounds off before the powder thaws."

I agree that typical temperature swings won't have too much effect, but some places get really cold and a round sitting in a hot chamber after some rapid firing could bring up the temp quite a bit. Long range could make the difference more apparent. The thing to remember too is velocity is tied to pressure. A handloader developing a fast load in cold weather might push over max pressure in the heat. Powder selection may give a better margin, but without pressure test equipment it is all still a guess.

Fortunately for my wallet, 6.8 ammo has come down to almost 5.56 prices so the test didn't hurt too bad. Those Gold Dots (bonded softpoints) are great rounds and running 12.99 at PSA

 

[68wj]

Update:
I wanted to revisit AA2200 with an additional data point for a moderate temperature, and more importantly a normal load. The 6.8 FMJ load was just enough to cycle the action for trigger time with Remington's boomerang bullets (ie, a lot of space in the case). I wanted 2 questions answered:
1: Is the velocity change more on the cold side, or hot, or is it linear?
2: Does a full pressure load fair better or worse from temperature change than the previously mentioned light load?

Data below, but my takeaway is that the velocity increase is relatively linear (thus predictable), and the full pressure loads buffer temperature's effect on velocity.

16" 6.8 SPC barrel, Hornady 110 HPBT bullets, 28.*gr AA2200, CCI41 primer


Data from previous test presented in a similar fashion. The light load had an almost double fps change rate.

 

[taliv]

the least temp sensitive powder i know changes about .5 fps per degree F and the most temp sensitive powder i know is about 1.7 fps per degree F.

i would like to see the tests carbine85 is referencing because his statements are totally contrary to everything i've seen.

not sure where the variation in your tests is coming from. and i'd bet the h322 test is a fluke and if tested again would show a much bigger difference

 

[pintler]

Thanks for the tests!

It's probably old hat, but one of the claimed advantages for the 'Superformance' powders is reduced temperature sensitivity:

"Superformance propellant design also produces very uniform performance in extreme weather conditions. Most Superformance loads lose very little or no velocity at low temperature and gain very little or no velocity at high temperatures. The performance and point of aim will not change drastically in extreme temperature situations. For a Superformance 30-06 150 gr SST load the performance was as follows;
+70 deg F: 3,071 fps @ 56,800 psi;
+140 deg F: 3,128 fps @ 61,400 psi;
-15 deg F: 3,022 fps @ 58,100 psi."

From http://www.hornady.com/assets/files/superformance-technology.pdf

 

[68wj]

the least temp sensitive powder i know changes about .5 fps per degree F and the most temp sensitive powder i know is about 1.7 fps per degree F.

...

not sure where the variation in your tests is coming from. and i'd bet the h322 test is a fluke and if tested again would show a much bigger difference

The temp variations were mostly within those figures. My latest is shown as variation per 10 degrees.

In this thread, another 6.8 shooter tested H322 in a temp range of 22-93*F. With a 110gr bullet the variation was 1 fps/10*.

 

[jmr40]

The .5 to about 2 fps velocity difference per degree is about what I've always read. Assuming most loads are developed at around 60-80 degrees and few shooters will actually be using those loads much above 100 or below zero the difference isn't that big of a deal until you start shooting over about 300 yards.

If -40 degrees or + 140 degrees is a possibility or extreme long range shots are possible then it can make a huge difference. That said if everything else is the same I'll always pick the least temp sensitive powder.

Regarding the Superformance ammo and temp sensitivity. I've read some reports that any manufacturers claims of powder being temp stable is limited to certain rounds. The Superformance powder sold to the public is formulated specifically for 30-06 and is very stable in that round. While it can be used in other rounds, the claims of better performance and temperature stability may not apply.

 

[68wj]

To clarify, this was factory Superformance .223 ammo, not handloads with Superformance powder.