What causes powder temp sensitivity?

[mwkelso]

I would be more concerned about the effects of heat on a loaded cartridge over the cold.
Sure your talking about slight POI differences & not safety issues.

In extreme cases I have heard of chambered rounds go off when the bolt closes due to chamber heat & also high ammo heat.
In extreme cases I have heard of chambered rounds go off when the bolt closes due to chamber heat & also high ammo heat.

In saying that you only have to think about anything that is kept in sub zero temps!
Car brakes can freeze so if you go by that then bullet weld could also occur, that alone would affect POI.

Fortunately we don't have too many major heat swings where I'm at. The coldest I've ever hunted was -14F, but that temp is rare. Typically we see anything from 20F to 85F through hunting season.

The safety issue definitely stands. I had been told not to load up to max when load developing in cooler temperatures, but never thought to ask why. Yours and one of the above answers just explained why that is.

 

[aushunter1]

I had been told not to load up to max when load developing in cooler temperatures, but never thought to ask why.

That makes total sense for any powder whether heat sensitive or not I recon.

I like to develop my loads on cooler weather(talking about 59F or a bit less) as the barrel cools down quicker in between strings. But the majority of my hunting is also conducted at around the same temp or even less.

 

[shinbone]

What causes gun powder to be sensitive to temperature changes?

I'm no chemist or gunpowder expert, but, in general, chemical reactions (which is all burning gun powder is) run faster at higher temperatures. For the situation of gun powder burning in a cartridge in a rifle, that means it will reach peak pressure sooner, which means peak pressure will be higher.

There could very well be other temperature induced affects as well.

 

[338 dude]

Agreed with the stable powder. Especially since I carry in the mag.
What makes it difficult to do? Is there a pretty quick heat transfer once the brass touches the inside of the chamber?

Not to mention the temperature of the barrel we all know how some barrels like to shift when they become warmer

 

[338 dude]

I would be more concerned about the effects of heat on a loaded cartridge over the cold.
Sure your talking about slight POI differences & not safety issues.

In extreme cases I have heard of chambered rounds go off when the bolt closes due to chamber heat & also high ammo heat.
In extreme cases I have heard of chambered rounds go off when the bolt closes due to chamber heat & also high ammo heat.

In saying that you only have to think about anything that is kept in sub zero temps!
Car brakes can freeze so if you go by that then bullet weld could also occur, that alone would affect POI.

I thought a round cooking off mostly would only happen in full auto machine guns and extended strings of fire Which is why many machine guns work from an open bolt rather than a close bolt

 

[ShtrRdy]

Several years ago I was using the Magnetospeed to measure velocity on some cartridges I had loaded and characterized in the summer. I wanted to get an idea of what the velocity would be when it was cold. The outside temp was in the single digits (farenheit) . The velocity I measured was faster than what I measured in the summer! I wrote to Magnetospeed and their answer was that this sort of behavior is well understood, blah, blah. End of discussion, as far as they were concerned. The only thing I could think of later on was that the barrel bore was a smaller diameter which would cause higher pressure and, therefore, higher velocity. Unfortunately, on that cold day, I only fired a few rounds. If I would have fired more to heat up the barrel I might have known if that was the case. Now I only use the Mag-speed when the temp is 32 degrees F or above.

 

[Jeffpatton00]

I would have to say, the temp of the steel would only have measurable effect on the burn rate of the powder. But I've been surprised many times by physics...lol.

LOL. I've been surprised by physics many times too, especially gravity...

 

[lotech]

Because of the temperature sensitivity of some powders, I've gone to Hodgdon Extreme powders exclusively with no regrets for all game hunting cartridges.

 

[mwkelso]

I thought a round cooking off mostly would only happen in full auto machine guns and extended strings of fire Which is why many machine guns work from an open bolt rather than a close bolt

I was thinking that and about the M1 Garande slamming down on a weak primer

 

[mwkelso]

Because of the temperature sensitivity of some powders, I've gone to Hodgdon Extreme powders exclusively with no regrets for all game hunting cartridges.

Same here. I'm also experimenting with RL23 in my 300WM. It's supposedly temp stable as well

 

[mwkelso]

Not to mention the temperature of the barrel we all know how some barrels like to shift when they become warmer

Maybe the steel is more susceptible to temperature change than we realize. If heat has the ability to make POI climb, perhaps it is because of flexibility change of cold steel vs heated steel. I'm sure it isn't much change, but maybe just enough to change how easily the barrel whips.

 

[pony doctor]

I was reading a thread about a couple of hand loaders that went hunting on a very cold morning and could not get their long range shots dialed correctly. They had left their ammo in the truck over night. The next day they, after they kept their ammo in the tent with them, their shots were hitting perfectly. They also wrote that they kept their rounds in their chest pocket until they were in their area and nearly ready to shoot.

What causes the sensitivity? Is it the temperature of the cartridge itself? Or are there more factors?
If so, could those who single feed choose any powder they want for their rifle as long as they use their body heat as a constant factor while working up a load and hunting/shooting it?

Question for the "gurus" of Ballistic Calculations. Example: My Sig Saur Kilo 2400 range finder uses formula's that incorporate temperatures and tables to input velocities recorded at variations in outside temperature. What is the "confidence" of these calculations to address environmental differences? Can we depend/rely upon ballistic "solutions" with confidence that our solution will be correct? These calculators also incorporate the specific powder used, so just wanting to know what those highly experienced shooter's confidence's may be. Thanks. John

 

[fguffey]

I have suggested reloaders put their summer reloads in the freezer before going to the range, I have suggested the summer reloader/winter hunter carry their ammo to the hot summer range in a cooler.

And then there is something we can learn from the successful ice fisherman; keep your worms warm.

F. Guffey

 

[John Klingenberg]

I never dealt with powder temp sensitivity when I lived in Texas. It's an understood rule across the state to not leave ammo on the dash or eventually you'll have a cook off. I was bad about it until I had a .308 break my lower windshield on a pleasant 112 degree day.
When I moved to Michigan I built a 6br in June. I worked up an awesome load with RL15 and it was a nice one hole rifle. Later I took it out on a nice January day using my June loads and it was shooting 3 inch groups. I went over all the screws, bedding, crown etc. Everything looked fine. Then the powder sensitivity occured to me. I swapped to Varget and 8208. No problems year around. I have some of the original loads left and they shoot excellent from May to October but anything below 30 it's a terrible load.