Effects of Temperature on Ammo

[SteelerNation]

Hi:

I have been learning long range shooting on my own since I started late last year and have been caught several times asking myself questions that I can't get an easy answer to.

One of those questions is the effect of changing ammo temperature on accuracy and precision. I store my ammo in my home in a cool (68-72 degrees F), dry, dark area. However, since I live in the Northeast, this means that in the winter I am moving it from inside to outside at the range where it can be very cold (today is 15 degrees F, for example).

What effect does this have on precision? I would assume that its a good idea to wait for the ammo temperature to equilibrate to the ambient temperature before starting any sort of shooting in which I am attempting to measure accuracy and precision (more so precision).

I'd like to hear what you guys have seen in your experience, as well as any tips to mitigate potential detrimental effects on accuracy and precision.

Thanks!

Mike

[sixonetonoffun]

I had a 7rm last fall shooting rem core-locts consistently at 1.5-2" until the temp went to 30-ish. Then it tightened up considerably. Made up some 270 rounds used h4831sc and found little to no variation.

[SteelerNation]

Found this on Field & Stream, although it really isn't very helpful. More or less just an observation


"March 18, 2014

Rifles: How Temperature Affects Load Accuracy

by David E. Petzal




11


Before we get to the real subject of this post, permit me to discuss life on other planets. According to informed sources, the number of these bodies in the universe is 10 to the 24th power, which reads 1,000,000,000,000,000,000,000,000. Given the immensity of this figure there is surely life of some kind out there, perhaps quite a bit of it. And no matter what form it may take, or how alien it may be to us, none of it can possibly be more horrible than Chris Matthews. Thanks for bearing with me.

One of the factors that is not given enough credit for making the life of the rifle shooter a living hell is the effect of temperature on the rate at which powder burns, and therefore on accuracy. I got a good taste of this last week when I went to the range with Old Sure Thing, my impeccably precise .30/06.
I was shooting a load which I had worked up last summer (you do remember summer?) involving a hot charge of IMR 4831. I remembered it as being very accurate, but the groups that showed up were not. Originally, it would put five rounds in .602, but a few days ago I was hard pressed to keep three shots inside 1.5 inches.
The joker was the temperature. My meticulous records showed that I had come up with this load in August, and that the temperature was in the mid ‘70s. On the day of the dismal groups it was 23 degrees, and that 50-degree difference was enough to screw things up royally.
There’s not much you can do about this except be aware of it. There are powders that are advertised as being insensitive to temperature, and you can try those, but the best approach is to keep track of how everything shoots and what the temperature is at the time.
If this doesn’t depress you sufficiently, I can point out that altitude can also do strange things to the way a rifle shoots, and you have to check that, too. It’s enough to drive you to flyfishing, which at least you do in warm weather, unless you fish for steelhead, in which case you deserve whatever happens to you."

[SteelerNation]

I think the only thing one can really "do about it" is to allow the ammo to come to ambient temperature and do enough shooting to know how it effects the particular load in question.

Any thoughts...?

[LoneWolf]

It seems to be that some powders are affected more than others, but all are affective to some degree. I saw about a 30FPS difference in my 308 using IMR4064 in 40* weather compare to 70* weather. Meaning I had to adjust my data if a match that started in the morning ended in the afternoon. I haven't played with it enough to verify for sure yet, but the Hybrid100V in my 243 seems to be pretty stable so far. Wish it was as easy as 1FPS per degree or something like that, but there is a way to calculate a temperature sensitivity factor. I have done a lot of research on it though because it hasn't been to big of a deal within 1000yds for me since I switched away from the 308.

[SteelerNation]

It seems to be that some powders are affected more than others, but all are affective to some degree. I saw about a 30FPS difference in my 308 using IMR4064 in 40* weather compare to 70* weather. Meaning I had to adjust my data if a match that started in the morning ended in the afternoon. I haven't played with it enough to verify for sure yet, but the Hybrid100V in my 243 seems to be pretty stable so far. Wish it was as easy as 1FPS per degree or something like that, but there is a way to calculate a temperature sensitivity factor. I have done a lot of research on it though because it hasn't been to big of a deal within 1000yds for me since I switched away from the 308.

LoneWolf:

Thanks. That's really helpful! I am trying to figure out to what degree ammo is effected, so your test is very helpful. I have read that some powder is designed so at to be unaffected by temperature variation. When I start reloading (very soon) I am going to keep a very good log book on the temperature and environmental conditions of when I made and tested the load.

I can imagine scenarios where a hunter (lets say) designs a great load for his rifle in the late summer, but when he goes out hunting in the late fall, the ballistics are very different! This could be very frustrating!

Thanks again!

[LoneWolf]

on youtube there is a series called "sniper101" by a tibosaurausrex I believe. I'm sure he discusses affects of temperature in at least one of the videos in his series. I've also notice him using a thermometer to check his ammo temperature in numerous videos.

[kevwil]

I wonder if accuracy changes due to temperature fluctuation are a result of changing harmonics due to the burn rate slowing down? Like if your 70F weather "accuracy node" could change to a "scatter node" at 20F.

[yobuck]

LoneWolf:

Thanks. That's really helpful! I am trying to figure out to what degree ammo is effected, so your test is very helpful. I have read that some powder is designed so at to be unaffected by temperature variation. When I start reloading (very soon) I am going to keep a very good log book on the temperature and environmental conditions of when I made and tested the load.

I can imagine scenarios where a hunter (lets say) designs a great load for his rifle in the late summer, but when he goes out hunting in the late fall, the ballistics are very different! This could be very frustrating!

Thanks again!

Tell you what, take a ride over to Pats and pick me up a couple cheese steaks and i'll tell you all you want to know. lol
And its a good thing you live outside and not in west philly with a name like that.
As for temp affects on ammo, yes it can be a problem for hunters and some more than others.
One of those things some might refer to as (something that happened to cause me to miss.)

[390fe]

If you're worried about temperature variations in your loads, simply switch powders.

The ballistics group at IMR has tested this powder from -40 to +165 degrees Fahrenheit with virtually no performance variation.

http://www.imrpowder.com/8208xbr.html

[LongRange]

If you're worried about temperature variations in your loads, simply switch powders.

The ballistics group at IMR has tested this powder from -40 to +165 degrees Fahrenheit with virtually no performance variation.

http://www.imrpowder.com/8208xbr.html

you do know that ALL of their testing is done indoors where most environmental's other than temp dont change right?

to the OP...ive shot(300WM)in the most extreme environmental's you can think of...now im on the west coast so maybe not as cold as you guys get but close enough. ive shot in light to pouring rain,light to heavy snow,9degs to 105degs.0 to 35mph winds and everything in between because like you i wondered the same thing and what i can tell you from all of that is that you need to go out and shoot in these conditions to know what changes weather has on point of impact. in my 300 70.5g of RL-22 in nosler brass with a CCI250 primer and a 208g hornady is good from about 70degs and up with slight elvevation changes regardless of conditions and 71g RL-22 in the same brass with the same primer is good from 9degs to about 60degs regardless of conditions. with that said i will tell you that rain and snow has a HUGH effect on POI...i shot one day in a light snow with the 71g load and had 6 hits out of 10 fired at 1010yds on 6" AR500 plate targets...the next day from the same place with the same load but heaver snow falling i could not hit the 6" targets but shot a 10" group on an 18" target.
an easy way to access temp changes on ammo is to go out on a hot day and pak a lunch box full of ice,put 5 rounds on ice,5 rounds in the shade and 5 rounds in the sun and shoot each group from a cool barrel....keep in mind ALL powders are temp sensitive(just some more than others) I dont care what ANYONE says its a fact!!

[yobuck]

you do know that ALL of their testing is done indoors where most environmental's other than temp dont change right?

to the OP...ive shot(300WM)in the most extreme environmental's you can think of...now im on the west coast so maybe not as cold as you guys get but close enough. ive shot in light to pouring rain,light to heavy snow,9degs to 105degs.0 to 35mph winds and everything in between because like you i wondered the same thing and what i can tell you from all of that is that you need to go out and shoot in these conditions to know what changes weather has on point of impact. in my 300 70.5g of RL-22 in nosler brass with a CCI250 primer and a 208g hornady is good from about 70degs and up with slight elvevation changes regardless of conditions and 71g RL-22 in the same brass with the same primer is good from 9degs to about 60degs regardless of conditions. with that said i will tell you that rain and snow has a HUGH effect on POI...i shot one day in a light snow with the 71g load and had 6 hits out of 10 fired at 1010yds on 6" AR500 plate targets...the next day from the same place with the same load but heaver snow falling i could not hit the 6" targets but shot a 10" group on an 18" target.
an easy way to access temp changes on ammo is to go out on a hot day and pak a lunch box full of ice,put 5 rounds on ice,5 rounds in the shade and 5 rounds in the sun and shoot each group from a cool barrel....keep in mind ALL powders are temp sensitive(just some more than others) I dont care what ANYONE says its a fact!!

See, your gettin some really good advice and your just not listenin. lol
Could it have something to do with not comin in out of the rain also?
How can you ever expect to make first round cold hore shots if your using the wrong powder?

[shooterfpga]

I use h4350 and imr4064. H4350 has .29fps/1* vs .53fps/1* with imr4064. Also take into account the primers used as well as other factors beyond your control that will change the temperature sensitivity factors. Its best to use atleast a 50* change in temp to shoot from. Some guys do this by cooling or heating ammo and immediately shooting them before the ambient temp can stabilize the ammo and the barrel heat affects it.

[LongRange]

See, your gettin some really good advice and your just not listenin. lol
Could it have something to do with not comin in out of the rain also?
How can you ever expect to make first round cold hore shots if your using the wrong powder?

im not sure what your trying to say here but i do make first round cold bore shots more often then not....

[Steelhead]

My 260 with H4350 is less than 50fps going from 100+ to low teens.
My 75bthp/8208xbr load is about the same.
My w748/69 SMK's load changes a lot but still remains accurate.

[sixonetonoffun]

I think it is helpful to understand temp sensitivity. Not only for the competitive shooter, but hunting as well. Conditions change and can effect accuracy easily by as much as 1-2" @ 100 yards. Granted inside 100 yards where most deer are taken it won't matter.

Neighbor had a guy in his party fly in from cali to hunt this fall. I chased a buck and doe towards him and @ 200-300 yards he was off by feet. No doubt temperatures weren't the only factor here.but definitely one he could have been better prepared for.