What causes powder temp sensitivity?

[rammac]

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

A cook off happens because the chamber is so hot that it heats up the powder in the cartridge and it ignites (something like 300 degrees F). So any time that the chamber gets up to around 300 degrees F you will have the potential for a cook off, regardless of whether it's a semi-auto, pump, or a bolt action.

 

[rammac]

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?

It's not just powder temperature sensitivity that has an effect on the point of impact.

The temperature sensitivity of the powder is controlled by the chemical composition of the powder and any coatings that may have been applied to control the burn rate and temperature sensitivity. What those chemicals are I don't know and doubt if you could found out what they are since most powders are proprietary. Colder air will also cool the temperature of combustion which results in less muzzle velocity and will affect the trajectory of bullet.

Air temperature also affects point of impact. Colder air is more dense which changes the trajectory of the bullet, basically cold air causes a bullet to drop quicker.

So colder air will cause the bullet to drop due to slower muzzle velocities and denser air.

 

[Rflshootr]

And now that we thought about powder burn rate changing and how temperature effects how hot things burn.........do you suppose that temperature might have an effect on how the primer compound might change in hot or cold temps? Now you know why short range bench rest shooters load at the match and tune their loads to the conditions.

 

[mwkelso]

And now that we thought about powder burn rate changing and how temperature effects how hot things burn.........do you suppose that temperature might have an effect on how the primer compound might change in hot or cold temps?

Absolutely! It would likely explain why non-magnum cartridges sometimes need a magnum primer in cold conditions, and vice versa.

 

[halfmile]

We had Pdog 223 rounds suddenly vaporizing the Hornady SX bullets we were using. Had them on the table in direct sun, and they were loaded just under 3400 FPS.....put them in the pop cooler and they started working properly again.

Apparently the warmup got them just over the edge, velocity wise.

HM

 

[Zymurgist]

What cause 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.

I'm not a chemist either but if you're interested there is a scholarly set of articles here: https://www.chemguide.co.uk/physical/basicrates/temperature.html

 

[HaroldNRAEndowment]

A cook off happens because the chamber is so hot that it heats up the powder in the cartridge and it ignites (something like 300 degrees F). So any time that the chamber gets up to around 300 degrees F you will have the potential for a cook off, regardless of whether it's a semi-auto, pump, or a bolt action.

I do not have experience in the following information, but I remember reading an article about 20 years ago where competitors would have a tube full of ice water to dunk the barrel in while competing. My first impression was certainly one would not want any water left in the barrel for safety. Unless the heat flashed the water off. I would be inclined to run a patch to make sure it was dry. As I am responding I wonder if the cutting fluid for machining centers would be a better solution due to the machine being made out of carbon steel, the cutting fluid is also non-corrosive and made to keep the machining cutter cool from over heating. Two things one would have to investigate, is it toxic and could ice cubes be made from it. Or maybe one would not have to cool the liquid if the liquid is getting hot enough to vaporize. When liquids change state from fluid to vapor the heat transfer can be multiplied 500 times.

 

[LVJ76]

I do not have experience in the following information, but I remember reading an article about 20 years ago where competitors would have a tube full of ice water to dunk the barrel in while competing. My first impression was certainly one would not want any water left in the barrel for safety. Unless the heat flashed the water off. I would be inclined to run a patch to make sure it was dry. As I am responding I wonder if the cutting fluid for machining centers would be a better solution due to the machine being made out of carbon steel, the cutting fluid is also non-corrosive and made to keep the machining cutter cool from over heating. Two things one would have to investigate, is it toxic and could ice cubes be made from it. Or maybe one would not have to cool the liquid if the liquid is getting hot enough to vaporize. When liquids change state from fluid to vapor the heat transfer can be multiplied 500 times.

We used towels that we would soak in water from the ice chests to cool down the barrels. This was and still is done when there arent many shooters in the match or if several shooters use the same rifle, this was done to maintain accuracy and not burn out the barrel. With towels no water gets in the barrel.

Shooting silhouette you fire 10 rounds under 6 minutes or less and when its 115 degrees outside the barrels take forever to cool down, thats if you call 115 degrees cool Lol.

I never saw anyone dip the barrel in water but towels are used still.

 

[Richard of Oz]

I'm not a chemist either but if you're interested there is a scholarly set of articles here: https://www.chemguide.co.uk/physical/basicrates/temperature.html

Well, at last someone has suggested referring to a knowledgeable source, rather than relying on the advice of opinionated strangers on the internet! A couple of you have suggested using temperature-stable powders like Varget and other so-called "Hodgden" powders. My suggestion would be to write to the people who actually make those powders, ie ADI Powders in Australia. They DO have the knowledge. I suggest you take this question to them.