Temp insensitive powders and barrel heat

[JFrank]

Shooting at 200yds this is the second 10 round target with the rounds "cooking", the first target they were all grouped around 1 1/4 inch. After I realized what was going on I just went with it to see what would happen. So temp sensitive powders are for ambient temps not accelerated temps cooking in the chamber. Sorry to sound dumb to this but until recently I was never able to get groups tight enough to notice these things making a difference.


View attachment 1108557

Might be wise to get a temperature strip for the side of the barrel.

 

[Ned Ludd]

I think that is the often interpreted conclusion, that a hot barrel causes the combusting charge to somehow burn hotter, and therefore raise pressure.

My conclusion is quite the opposite. That the relatively cold barrel quenches the burning charge REDUCING pressure. This is, and I think I'm correct in stating this, a law of thermodynamics. That if you cool a gas in a confined space, it will reduce in volume and therefore pressure. And a cooler barrel will quench the gas charge more than a hotter barrel. It is an indisputable fact that heat from the burning charge is being transferred to the barrel during ignition.

Shooters work with this effect by warming the barrel before shooting for record, and allowing as much cooling time between strings as necessary to keep the barrel within the best operating temperature range.

In the study I reference above, the barrel was not allowed to go above a certain temperature, so it would be interesting to see what happens if the barrel is allowed to continue to heat. Would the rate of pressure rise continue to rise proportionate to the barrel temp rise? Or would it plateau, and if so, at what temperature?

At some point you'd get cook-off of the round, but that is typically the primer detonating. What if the bullet is chambered and fired quickly, before primer cook-off can occur? Its burn qualities must be effected by temperature of the primer compound, in fact the author of the above study ends his paper by bringing up this very subject. Is it primer temperature, and not barrel temp that has the most effect on pressure rise?

Inquiring minds are sure to find the answer.

A hot barrel won't change the total amount of energy released by combusting a given amount powder, but it will increase the rate at which it burns, and therefore the rate of gas expansion. For practical purposes, the effects are all relative to ambient temperature. Because combustion is nothing more than a chemical reaction, a hot barrel (relative to ambient) should have a net increase on burn rate, a cold barrel (relative to ambient) should reduce burn rate as you noted. However, powder burn rate, pressure, and velocity are not linear with respect to time. To be honest, I'm not sure whether the burn rate values we typically use are extrapolated instantaneous values, or are time-averaged values, although I suspect the former. To make things more complicated, pressure values are typically peak values, and velocity is measured at the muzzle, neither of which occur at exactly the point of maximum powder burn rate, but slightly after.

Although barrel heating relative to ambient would be most commonly observed during typical shooting practices, I can imagine instances where it might go the other way. For example, loaded rounds that had been accidentally left out to cook in the sun for a while might show lesser velocity out of a barrel at ambient temperature than out of a hot barrel. People have carried out a variety of experiments to determine the effects of temperature on powder burn rates. My point was simply that heating or cooling a loaded round itself is only part of the effect of temperature on powder burn rate. Unfortunately, this seems to be the way powder temperature sensitivity tests have sometimes been conducted by manufacturers in the past. I believe the effect of barrel temperature (i.e. the chemical reaction vessel) cannot be ignored or removed from the equation as a significant amount of the propellant burns outside the case.


For those that are interested, below is a link to a thread at another shooting forum involving various powder burn rate-temperature experiments. It is 10 pages long, but I thought it was a very good read.

https://68forums.com/forums/showthr...ensitivity&s=295c09a40a9f5276286769590e71e055

 

[Lefty Trigger]

Might be wise to get a temperature strip for the side of the barrel.

I actually bought a 10 pack of those and as soon as I remember where I put them I'll get one installed. If I remember right the max temp not to exceed was 140 degrees and I think the temp strips were 85 to 140 range,... now if I could just find them...

 

[simo hayha]

Either speed up or slow down your shooting process. Both require the shot tobe taken with the shortest amount of loaded chamber time.

 

[Sandstorm]

Mikea says
I live in the desert and 100 degrees by 10am. How about a cartridge straight from the cooler. Hot barrel and cool round. Silly?

Ive also been playing with that here in the Desert, with rounds out of my cooler into a Hot barrel during a Match.
I dont think it hurts anything, and may help some...its been too windy here to tell for sure but ill keep
messing with the cold ammo to see if there's any benefit.

 

[Texas10]

I think that if you developed your load with chilled rounds and shot in hot temps with a hot barrel, you are doing everything you can to maintain control over powder temps and burn characteristics.

I've got a battery operated air pump that does a great job of cooling the barrel down to ambient in the hot Texas summers. I may have to add a cooler to my already too heavy range box....LOL

 

[284winner]

Mikea says
I live in the desert and 100 degrees by 10am. How about a cartridge straight from the cooler. Hot barrel and cool round. Silly?

Ive also been playing with that here in the Desert, with rounds out of my cooler into a Hot barrel during a Match.
I dont think it hurts anything, and may help some...its been too windy here to tell for sure but ill keep
messing with the cold ammo to see if there's any benefit.

I was doing that years ago in competitions with ice packs. Wrap soft ice packs around my ammo boxes during the shoot. Kept all the ammo at a cooler temperature without overheating. Not sure what people do today. Maybe put the boxes in coolers.

 

[Sandstorm]

Now if I could just get a little help with the wind out here in Arizona, I might do a little better than a 579...ughh
Oh well some days are better than others, and some downright depressing. lol

 

[243winxb]

https://apps.dtic.mil/dtic/tr/fulltext/u2/a361433.pdf Army research Lab. testing, wants to keep the barrel temperatures down.

https://discover.dtic.mil/



Look at powders SDS or MSDS to see it it contains one or more of the above additives?? I have not checked.
https://www.hodgdon.com/wp-content/uploads/2019/01/2019-extruded-rifle-powders-adi-sds.pdf

IMR powders https://imrpowder.com/resources/safety-data-sheets/