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Old 01-24-2013, 13:23   #17
TDC20
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Quote:
Originally Posted by Any Cal. View Post
In my looking on BD inverse sensitivity, it appears that in very cold conditions the granules fracture, making them smaller and removing any coating on one side of the kernel, both of which contribute to a faster burn rate. It seems like the process is irreversible, so once the powder had been exposed to extreme cold, it would be a faster powder regardleess of temp. Might make a good experiment to put a few rounds in the freezer overnight, then chrono those that had never been frozen, those frozen and thawed, and those that were still cold.
This would be an interesting experiment to try.

I have also wondered about what effect humidity absorption has on burn rates, velocity, pressure, etc. When I began handloading, I read everything I could on the subject, and I remember reading that powders are hygroscopic, which means that they absorb water from the air in the same way silica gel dessicants do. That's why it's not recommended that you leave powder in your powder measure and always keep a tight seal on your containers. I have, on occasion, forgot to return the little bit of powder I had in the powder trickler for a day or two, and dumped it back in the container anyway. Not a good practice, I know, but I'm a cheap bastard. So, what happens when a powder absorbs moisture? Does it run slower because it weighs more so you use less, or faster because it has the added expansion of the water vapor adding to pressure? Or maybe it's a zero sum process. I'm assuming that it could also lead to reliability problems if it gets exchanged to water vapor and re-absorbed during temperature cycling. Any thoughts on this?

The reason I ask is that this was the end of my first pound of BD, and it has been around for a while. I didn't leave it sit out, but the container has been opened and re-sealed a bunch of times, so it could have more H2O content than a freshly opened batch.
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