Hey Guys,

Does anyone know what causes some powders to be temperature sensitive.

I reloaded some 280 gr. Swift A-Frames in my .35 Whelen in front of RL-15. It was March and the temperature was in the 40s. Capped of about 50 rounds. No signs of pressure, what-so-ever.

In July I repeated the loading I had done in March. The temperature was in the mid 90s. After the 3rd shot I was blowing the primers out of their pockets. My gunsmith said that the RL-15 is temperature sensitive.

To repeat my question, "Does anyone know what causes some powders to be temperature sensitive?"

Thanks,

Smoker

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Never piss in a man's face unless his beard is on fire.

More than likely you were past max for your particular gun and as the brass became work hardened, your cases started to go....Tempature does not have that much effect of brass cases, overloading does. This old rumor continues to exist IMO..

If the temp does cause problems then you were to hot to start with....I load and shoot in way below 0 in Idaho and in the hottest Africa has to offer with RL-19, RL-15, 4350, 4831 for the most part plus a few others, and have not had any problems...but I normally shoot a gr. below book max or so depending on the rifle, or lets say below the particular rifles max...Once a rifle reaches its max then adding grains of powder will only produce about 10 to 15 FPS increases, so nothing is gained by pushing the envelope.

In my 338, I am right at pure max and still have not had a problem with H4831 or RL-19....

Hey Ray,

The cases were new on both days. On that particular March day I was testing the velocity of the load. On the July day, I was just just out to the range to socialize. Both times I had loaded new brass. My gunsmith said that maybe I was right at the point of excess pressure where temperature made a big impact. He also told me to back off a few grains.

This is an interesting dilemma.

Thanks for your response,

Smoker

I thought you were looking for the scientific explanation of higher pressures in heat. That is common to all propellants except some are affected more than others. I've done quite a bit of chronographing where I develop my hunting loads, which is quite hot in the summer, and where I mostly hunt, which is Wyoming and Montana in the late seasons, around November.

Most powders slow down quite a bit in the cold. Loads I fired at home in the 70's, lost almost 200fps in freezing weather in Montana. That was with RL22 in a 338. I went to the Hodgdon Extreme powders and they seem to not be nearly as sensitive to the cold as the Alliant powders, but they do react to heat over 70�. With H4350 the velocity loss in freezing weather was negligible, around 25fps as I recall. I haven't found one Powder yet that didn't increase pressure and velocity in heat, and that includes the Extreme line of powders. I carry a digital temp gauge to all my shooting sessions and note it on targets and you can see the marked change when the temperatures get over 70 degrees and into the 80's or higher with the same loads. I'm sure there is a scientific expanation for this, but I don't care what it is. I know it happens. I also know that for Alliant powders in the cold I have to add a grain or two to the load to equal what I get at the range in warmer weather.

Another line of powder that seems to do well in cold is the Ramshot line. An outfitter friend, who is also a shooter and a gunsmith, has tested this line in Wyoming and it doesn't lose much velocity, even in extreme cold. I don't know what it does in heat, but I'd expect it to shoot up on pressure and velocity as they all do. Wish I could get that powder out here as it seems to be a good one.

Hey Bob338,

So what you're saying is that in warmer temps. back off the powder. During cooler temps. it may be okay to try something a little hotter. The powder I was using was RL-15.

I had tried about 4 other powders to get the velocity and accuracy up. With the RL-15 in Feb. I was gradually increasing the powder with no signs of pressure. During that March I had filled the case and figured I'd better stop. I was getting frequent one hole, 3 shot groups.

During that July the first 3 shots were around 2 inches and after that I wasn't even hitting the target - and I was blowing the primers out of their pockets. I used the same powder quantity, primers and new cases. I was absolutely baffled! I thought I had screwed up my rifle.

The reason I asked the question was to find out why some powders are more temperature sensitive than others. I've read posts on this forum about having problems with their powders with powders that were attributed to temperature. I've reloaded for over 20 years and this was the only time I had ever experienced any problems with blowing the primer out of its pocket.

I really like RL-15. According to my Chrony I was getting 2,547 with that 280 Swift A-Frame in my .35 Whelen. The accuracy was absolutely excellent. I put everything in the past tense because last May I messed up my back really bad and haven't been to the range with a rifle since.

Thanks for you insights, Bob.

Good shooting,

Smoker

Basically when things burn, they heat up and the warmer they are to start, the faster they burn.

Look at it like this: The same powder acts like a faster powder when it starts off warmer. The degree with which this affects different powders varies, and is not easily predictable. The pressure goes up exponentially with powder addition, so a little more powder (or a little faster) gives a lot more pressure.

This is one of the many reasons why published data may seem mild to some, hot to others, and wildly variable in extreme cases. You can also see this if you leave a loaded cartridge in a warm chamber. The cartridge rapidly warms up to the temperature of your barrell......