Hello All,
I was at the range yesterday - the weather a balmy 6 degrees F - testing some loads I had worked up for my 416 Weatherby Magnum using RL 22. After the 35th round, I realized that my efforts might be for naught if there was a significant effect on what a "maximum" laod might mean at this temp vs. at 100F.
What have your experiences been, especially with Reloder 22, in large calibers?
Thaks in advance,
Paul

Chamber temperature and powder temperature are two different variables that influence pressure and muzzle velocity. I've done tests with Varget and H4350, in an '06 size case, and in that case, the effect of chamber temperature is much stronger than the effect of powder temperature.

After 35 rounds, the effect of chamber temperature is likely to be substantial.

Never thought of that - even more food for thought, not only now, but for future load development. Based on your experience, how much time do you think necessary to get the chamber temp back to something that has little influence?
Paul

I have a little thermocouple that I just strap on the barrel, just ahead of the receiver. I fire a few shots to get the barrel up to about 15-20 degrees above ambient. Then I do all my load development at constant barrel temperature, give or take a degree or two. I just wait until the barrel cools to my target reading, and pop off another shot.

that after the 10th or 15th round, any effect of ambient temp (in this case, cold) has little effect on chamber pressures since the chamber temperature is substantially higher - in this case, nearly too warm to touch?
Thanks, this has been truly enightening. 27 years of reloading and I never gave this any thought.
Paul

If you want to ignore powder temperature, there is a simple way. Just chamber the next round as soon as you fire. If the round sits in the chamber for 3 minutes or more, while the barrel comes down to temperature, the powder will be close to the chamber temperature. Then ambient doesn't matter, and initial powder temperature doesn't matter. The only variable is chamber temperature.

The only data I have seen w.r.t. temperature variation was related to IMR powders. There, each degree change in temp resulted in 1.3 fps change. I suppose one could convert that to pressure using the pressure to velocity change rule of thumb (for easy math, say 3 to 1), which would mean about a 0.1% change in pressure for every degree change.

Just back of the envelope calculations, don't bet your life on it! FWIW, Dutch.