Effect of humidity on powder during reloading?

[Ruslow]

OK .How much does humidity play in the effectiveness off powder ie. say you left it in the scale for a few days before reloading again in say a high 75% or more humidity area. vs say in winter when the humidity is relatively low? now this is more than likely a non issue, but started thinking. Stan

 

[Sniper266]

This is an interesting question and i hope someone here can provide a good answer!

I would imagine that the effect would be minimal with regairds to the amount of humidity on powder and even in a loaded cartridge. The immense heat and pressure caused from firing a round is pretty great.
That being said; i dont think it’s unreasonable to theorize that rounds loaded in high humidity will be slightly slower than rounds loaded in zero humidity.

 

[supercorndogs]

Powder is hydroscopic. The longer it sits out in humidity, the more water it will absorb. This will make a smaller volume of powder weigh more.

 

[Rhed]

Me? I trust no weather. Weather, temp, humidity? You will never know what it’ll do to powder. Even our precious reloading tools. I never leave powder stored in a hopper. I put back in the original container when I’m done. all stored in a big plastic container bought from tj-max with other different powder brand containers. And leave a moisture pack inside the tj-max container too. Well, that’s what I do. Others probably have other means of storing powder effectively. Powder is expensive these days...

 

[DannC]

I posed this question several years ago on the GlockTalk forum. The most telling response came from a man well know in the handgunning world.
He lives in central Florida and loads thousands of rounds every month most often in raining weather in an unheated or air conditioned garage.
He claims that he sees no difference in rounds loaded in dryer winter months or in the wet summers, but these are primarily handgun rounds.
I do not think it is wise to leave powder or primers in your press if not actively reloading.

 

[Yankee88]

I have found results consistent with what supercorndogs said. I was being lazy, left powder in the hopper and reloaded the rest of my rounds a week later. My setup is in the garage no AC and was in late spring. When chronoed, they were noticeably, but not critically, slower than the rounds I first loaded. Also noticed storing powder in the garage vs inside made some velocity differences. Always store inside in controlled environment.

 

[Sheldon N]

Powder is hydroscopic. The longer it sits out in humidity, the more water it will absorb. This will make a smaller volume of powder weigh more.

Yep, someone recently did a test on this. Put some powder in a food dehydrator for 45 minutes then compared. The powder that was dried was a LOT faster, something like 100 FPS if I remember right.

I keep powder indoors in a climate controlled environment, only take it to the reloading room in 1lb increments when I’m using it.

 

[JayB]

There is an article in TFB recently covering this issue. They quoted a test by VV and concluded "keep your powder dry, but not too dry"

https://www.thefirearmblog.com/blog/2018/07/23/wisdom-from-vihtavuori-powder-moisture-content/

 

[Fig]

I agree with all that, and I believe both the Lyman book and several others warn not to leave powder in the hoppers. I will say this, however, I have hard, painted cardboard kegs of powder at least 60 years old that’s still good, and I still used it. It has always been stored in a dry place, but it certainly isn’t “sealed”.

 

[Milo 2.5]

VV recommends powder be stored under 68 deg in 55-60% humidity. Drying powder out is way more of a concern for me, I've seen some drastic changes in H4831, Varget, and when RL 23 & 26 came out, it was downright dangerous if it even dried out a little.
Some powders just being exposed to air, moist or dry starts to break them down and potency is lost< VV N 500 series

 

[supercorndogs]

I agree with all that, and I believe both the Lyman book and several others warn not to leave powder in the hoppers. I will say this, however, I have hard, painted cardboard kegs of powder at least 60 years old that’s still good, and I still used it. It has always been stored in a dry place, but it certainly isn’t “sealed”.

I found a rusted can of 3031 that had been sitting outside by a creek at a wildlife area, for at least 20 years. One day my girlfriend picked it up and asked me about it. She shook it it it sound like there was still powder in there. We went to the pickup and removed the rusty lid with some pliers. The can was smashed but had remained sealed. The powder looked and smelled normal. I put a lighter to it, and it burned. I kind of wish I would have loaded one round with it. I used 3031 in my 22-250 for 40g bullets then even.

 

[Deleted member 113831]

It is my belief that some of the variations people see between lots of powder, are simply because the "new" powder has not had the opportunity to acclimate to the same conditions as the "old" powder that had sat in the cabinet for awhile.

I had a couple of "fast" cans of Varget that were new and I adjusted my load for them. After six months in the cabinet I had to adjust it back.

 

[mdmp5]

Yep, someone recently did a test on this. Put some powder in a food dehydrator for 45 minutes then compared. The powder that was dried was a LOT faster, something like 100 FPS if I remember right.

I keep powder indoors in a climate controlled environment, only take it to the reloading room in 1lb increments when I’m using it.

This is correct. I read the article too, and the closing statement was something like, “keep your powder dry, but not too dry”.

Ideally you want your powder to contain the humidity of a cool environment, maybe 60% humidity. More or less room temp. Leaving powder exposed for extended periods of time will definitely increase the moisture content and should slow it down some

 

[mdmp5]

Shit I basically repeated some of what was written above. Didn’t see it the first time around

 

[supercorndogs]

It is my belief that some of the variations people see between lots of powder, are simply because the "new" powder has not had the opportunity to acclimate to the same conditions as the "old" powder that had sat in the cabinet for awhile.

I had a couple of "fast" cans of Varget that were new and I adjusted my load for them. After six months in the cabinet I had to adjust it back.

I haven't seen it, but it makes a lot of sense.

 

[hertz654]

Norma also has researched the effects of humidity (moisture content) on powder; short article can be found here: http://bulletin.accurateshooter.com/?s=humidity&submit=Search