Powders volume vs cold weather


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627PCFan
December 5, 2007, 12:25 PM
Im loading 7mm rem mags is 64 grains of IMR 4831. I worked the load up this summer in 80+degree heat and 75% humidity, shot real well. Now my groups are opening up as it gets colder. My powder charges are exact. Does the temperature affect the powder that much, or is it another variable I'm not taking into account?

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DogBonz
December 5, 2007, 12:33 PM
temp does effect velocity. It also can effect the heat distribution of your barrel.

rcmodel
December 5, 2007, 12:35 PM
It can.
Some powders are more temperature sensitive then others.
IMR-4831 happens to be one that is, I think.

But maybe you are just shivering more when shooting groups then you were at 80+! :D

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rcmodel

K3
December 5, 2007, 01:48 PM
rcmodel:

What about IMR4895, IMR4064, H335, and Varget? That constitutes my powder supply for rifles.

How sensitive is IMR 4831? I happen to really like that powder for most of my bolt action cartridges in the medium and above range. I loaded most of my ammo in the evenings in 75 degree weather and did most range work at temperatures from 55 to about 78. Didn't really notice much difference in that range. I have been hunting in weather in that type of weather too, though one weekend it was no more than 35.

rcmodel
December 5, 2007, 02:07 PM
Varget should perform well in cold weather.
It was the first of the Hodgdon "Extreme" powders designed to perform well at low temperatures. They have since changed several other of their powders to the "Extreme" formula.
http://www.hodgdon.com/smokeless/extreme/page2.php#top

How much of this is BS, and how much of it is true I don't know.
However I did see some test results in Handloader magazine when the "Extreme" line was introduced that seems to prove it really is much more consistent then many other powders at low temperature.

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rcmodel

snuffy
December 5, 2007, 02:44 PM
Now my groups are opening up as it gets colder.

Define "colder". Right now it's 25 degrees with bright sun on the fresh fallen snow. Last night it got down in the single digits.

Now that much temperature variation would definitely make a difference. As far as the Hodgdon claims of "extreme" powders goes, I just don't know. I use a lot of it, mostly because it works good otherwise

Wildfire
December 5, 2007, 09:57 PM
Yes temp. can and may change your POI. Hunters do not seem to notice this as much as target shooters, but every 10 degrees will change your velocity to some degree. Loading Max loads in cold weather is equally bad when using that same load in hot weather.
I run many loads through a chronograph on a regular basis. The temp will change the velocity sometimes daily. Humidity and eliavation will also.

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