Keep your powder dry

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Corjack
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Keep your powder dry

Post by Corjack »

I have heard this for years. Dry powder loads are faster than loads with higher moisture content. It seems to be popping up more frequently as a point of discussion. It would mostly benifit high volume shooters rather than hunters, but interesting none the less. Basically some lot to lot inconsistency can be explained by different moisture content. One fellow shooting Varget in a 6BRA, got an average of 2887 fps with powder right out the jug. He then placed powder in a dehydrator set at 105 degrees Fahrenheit for 30 minutes. Then had an average of 2929. Still studying this, as I am bit sure it is worth the bother. Also to note , powder is weighed, so low moisture content means a bit more powder in the case.
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slugslinger
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Re: Keep your powder dry

Post by slugslinger »

My experience matches your findings/hypothesis. This concept can become quite important if you are dealing with true maximum loads (not necessarily the "max" from commercial load tables). I live in Colorado at 6700 ft. where we generally have low humidity, and especially so with AC in the summer and heat in the winter. So my powder is going to dry out over time - because every time I open the container, some "dry air" is introduced.

A few years ago when IMR 4955 was first introduced, I was using it to develop loads for 300 Win Mag. Without introducing too much complexity to this explanation, suffice to say I was over two grains below Hodgdon's load maximum (another testimonial why you should always start low when performing load development). Yep, pancaked primer, stiff bolt lift, and a very noticeable ejector imprint. I double checked my load profile, and I would have guessed I screwed something up . . . except my buddy had the same problem (same lot # of powder).

I sent an email to Hodgdon, and got a very nice response from one of their ballisticians. I asked if there was a recall on that batch of IMR 4955, because something was really wrong. He said "no recall", but that batch was indeed at the hot end of the acceptable specification margin. Then we got into the conversation about powders drying out. He suspected that the "hot batch", and my dry climate and high elevation had both contributed to my experience.

A few handling tips:
* As always, store powder (and ammo) in a stable, cool, dry place (e.g.: seasonal thermocycling in a garage is bad!)
* Use your 8lb keg to fill a 1lb bottle for use (reduces the repetitive impact to the 8 lb keg)
* Be conscious of your ambient humidity - the reverse of all this is true if you live in a high humidity area
* Try to know where and how long your powder was stored before you purchased it (not always possible).
* (Related) Temperature aggravates the problem: load development vs actual use (if you develop max loads in 65 degrees, and then it sits in a hot car and is then fired at 98 degrees . . . you may exceed the margin).

Powder manufacturers actually have a specification for ideal powder humidity, and as you might guess, it is not extreme in either direction.

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