Temperature and gunpowder!

[RUMLUVER]

Has anyone out here had any problems with gunpowder being teperature sensitive. I heard powders from Alliant and IMR are sensitive to temp changes and will shift point of impact. Looking for anyone who may have had this problem. I currently use RL22, RL25, IMR 7828, H4350, and H4831sc for all my hunting loads and have found no evidence of this. So if anyone has tell us about it.

[Rapier]

I live in NW Florida and our winter weather here is rather famous for freezing at daylight and being 75 degrees by dark or the other way round. The wild variations in temp can cause considerable worry. I have not found H-4350 or H-4831 to be very temp sensitive and use both for that very reason.

Having said that, use a little reason, you can not develop a max load at 20 degrees and expect to have round primers at 100 degrees. I try to do my load development between 60 and 85 degrees.

[Rocky Raab]

Some powders are more temperature than others. Some are specially formulated to be less so. Examples are:

The Hodgdon Extreme line

Ramshot powders

RL-15

You may not notice much change, even when using other powders. One rule of thumb says that velocities will change about 10 fps for every degree from the temperature when the load was developed.

If that rule holds (and I cannot verify that it does) then it would take a 30-degree shift to change velocity by 300 fps.

[Jack]

Frankly, it's been my experience that temperature sensitivity of powder has been much overblown lately.
Living in Upstate NY, I see temps in the single digits (even below zero F, occasionally) up to the 80's and 90's.
I would agree with Rapier that it's wise to develop loads at more moderate temperatures- who wants to work up loads in the cold, anyway?
Rocky, I am, shall we say, extremely sceptical of that temp/velocity change formula. My chronograph shows much less difference- and I have chronographed loads worked up in the summer at winter temps. I rarely see more than 100 fps variation, if that. And I pay no attention whatsoever to whether a powder is 'temperature sensitive'.
One man's opinion- your mileage may vary.

[Rocky Raab]

Frankly, I'd tend to agree with your numbers too, Jack. As I said, I can't verify that the "rule" holds.

I also agree that the whole thing is overblown - unless you develop a max load at 20 degrees and then take it to Wyoming for summer prairie dogs!

THAT could get interesting!

[Ol` Joe]

There is a artical here http://www.shootingsoftware.com/tech.htm that answers some of the question. The author has a few other good articals posted here also.

[Paul5388]

The amount of sensitivity is going to depend on how much (like percentage) nitro glycerin the powder contains. The cooler nitro glycerin gets, the less sensitive it gets. So, you will probably find single based powders are affected less than double based powders.

With the forced split of DuPont and Hercules before WWI, DuPont took the single based powders and Hercules took the double based powders. To this day, DuPont (IMR) only has two double based powders (700X and 800X).

I would think the proper temperature to develope loads, to ensure there isn't a pressure problem, would be at higher temperatures. All the lower temperatures are going to do, if anything, is slow things down and lower pressures. It should be a pretty simple thing to zero the load in the cooler temperature ranges.

[denton]

When it is cold, your rifle and your ammunition are big "heat sinks" that rob energy from the propellant gasses. It turns out that the temperature of the rifle is about 3X as important as the temperature of the ammunition. As your rifle warms from shooting, you'll see pressure and muzzle velocity rise.

As nearly as I can determine, the mechanism behind temperature compensating powders is that they burn faster when pressure is lower, so the quickness of the powder changes with temperature, offsetting the loss of energy.

The good news is that when temperature compensating powders work, they can work pretty well. For me, Varget gave practically perfect temperature compensation in my former .308, with a 46 grain load.

The bad news is that a powder that is well compensated in one cartridge may be poorly compensated in another. Most likely, this is because each caliber has its own amount of case volume, casing and bullet mass, and relative surface area exposed to the barrel steel. In the 223, Varget gives me terrible (lack of) temperature compensation. It is more temperature sensitive that commercial "military" rounds sold over the counter.

So, net of nets, when it works, it works. Quite often, it doesn't.

[royinidaho]

Originally posted by RUMLUVER
Has anyone out here had any problems with gunpowder being teperature sensitive. I currently use RL22, RL25, IMR 7828, H4350, and H4831sc for all my hunting loads and have found no evidence of this. So if anyone has tell us about it.

I use RL-22 extensively. In the 270 Win velocity from summer (80s) to winter (0s) velocity lost is roughly 130 fps.

Ran a test last week with the 338 Win. 74.8 gr RL-22 WC 252 & Sierra 250 GK. Summer/fall velocity is 2800 +/- a few. Very low SD.

Set the loads on the wood pile over night put the rifle in the garage then moved to outside @ daylight.

Allowed everything to stabalize at Zero Degrees.

This is NOT a typo: velocity was 2900 FPS with very good SD.

Was major supprised. Figured chrono was out of wack.

Ran the 222: Velocity was spot on.
Ran the 270: Velocity was spot on.

270 loads were a way different lot of powder.

Ran 5 loads through the 338 very rapidly to heat thing up, and had put a cartridge in my shirt pocket to get it warm. When I figured it was warm I ran the 5 through then chrono'd the warm one.

Yep, velocity went down.

That is exactly bass ackwards

Makes for a fast shootin' 338 Win but groups were a little large and too far up and to the left. Rifle shoots 1/4 MOA @2800.

Someone gimme a hint!

[RUMLUVER]

I too have never heard of an increase of velocity with colder temps. Must be an annomoly or something else a fluke maybe.