What causes powder temp sensitivity?

[mwkelso]

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?

 

[elkaholic]

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?

Thats pretty much it. Temp swings vary with different powders and there is considerable difference in some of them. Duplicating temp they were chronod at is great but difficult to do. I have carried them next to my body before for that reason. The best bet is to use a stable powder like H1000

 

[mwkelso]

Thats pretty much it. Temp swings vary with different powders and there is considerable difference in some of them. Duplicating temp they were chronod at is great but difficult to do. I have carried them next to my body before for that reason. The best bet is to use a stable powder like H1000

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?

 

[elkaholic]

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?

Chamber temp can change powder temp pretty fast. You can have a normally safe load on a given temp day get dangerous when left in a hot chamber too long at a shooting session. Thats something to consider when testing loads.

 

[mwkelso]

Chamber temp can change powder temp pretty fast. You can have a normally safe load on a given temp day get dangerous when left in a hot chamber too long at a shooting session. Thats something to consider when testing loads.

I hadn't ever thought of that. Thanks for the insight!

 

[ShootMo]

I'm curious about the physics and chemistry behind the changes in pressure. It's clear that ignition is hindered in relation to temperatures below the sighted-in temperature. But does anyone know what the chemical composition difference is between temp-stability levels in powders?

 

[mwkelso]

I am curious to know if the temp of the steel has anything to do with varying POI in addition to the burn rate changing muzzle velocities?

 

[Chuckrub]

powder manufacture
http://www.scielo.br/scielo.php?script=sci_arttext&pid=S2175-91462015000400398

 

[ShootMo]

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.

 

[mwkelso]

powder manufacture
http://www.scielo.br/scielo.php?script=sci_arttext&pid=S2175-91462015000400398

Interesting to know how spherical powders are manufactured. I'm guessing that the simple answer to our question is that external temperature affects the rate at which the chemicals in different powders react to ignition?

 

[LVJ76]

I shoot silhouette competition, the ranges are 200m, 300m, 385m and 500m, and we dial and check each distance before the match starts, this happen at say 8 am and matches usually start at 9 am. Before temp stable powders came out we knew to adjust as the day got warmer, so lets say you started the match shooting at the javelina silhouettes at 300m you dial will be right on but by the time you got the rams at 500m say 4 hours later your hits can be 4" to 6" high when the temps rise to 90 or 110 degrees. So before we shoot our strings we adjust the scope on advance, dial down anywhere from 4 to 7 clicks and good to go.

We also experience this with smalbore silhouette, the 22lr ammo also has this issue.

However there is a solution for this, just like some hunters keep the ammo close to their bodies in the cold weather to keep it warm, we keep our ammo on a small cooler with ice packs, keeps it cool and there is no water so the ammo don't get wet.

Sometimes the temp stable powders aren't as accurate so got to use what groups best and in my case it's IMR-4350.

 

[mwkelso]

I shoot silhouette competition, the ranges are 200m, 300m, 385m and 500m, and we dial and check each distance before the match starts, this happen at say 8 am and matches usually start at 9 am. Before temp stable powders came out we knew to adjust as the day got warmer, so lets say you started the match shooting at the javelina silhouettes at 300m you dial will be right on but by the time you got the rams at 500m say 4 hours later your hits can be 4" to 6" high when the temps rise to 90 or 110 degrees. So before we shoot our strings we adjust the scope on advance, dial down anywhere from 4 to 7 clicks and good to go.

We also experience this with smalbore silhouette, the 22lr ammo also has this issue.

However there is a solution for this, just like some hunters keep the ammo close to their bodies in the cold weather to keep it warm, we keep our ammo on a small cooler with ice packs, keeps it cool and there is no water so the ammo don't get wet.

Sometimes the temp stable powders aren't as accurate so got to use what groups best and in my case it's IMR-4350.

Good to know, thank you.
I've never shot competitively, just target for sighting and hunting. Are the temperature adjustments a constant that can be calculated in the field? Or is this something that becomes second nature after shooting many matches?

 

[LVJ76]

Good to know, thank you.
I've never shot competitively, just target for sighting and hunting. Are the temperature adjustments a constant that can be calculated in the field? Or is this something that becomes second nature after shooting many matches?

I learned it from my dad and I've been shooting silhouette for over 30 years now, so now its like second nature but its also knowing your loads and how your rifle shoots them. This also applies for target shooting but hunting not so much for me since its done in cooler weather but not too cold where im at.

Once you know how your load performs at a given temperature you know what adjustments to make in advance without losing a couple of shots that might affect your score.

 

[aushunter1]

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.