Humidity and powder weight

[smokindog]

I've been poking around looking for information on humidity and powder weight. Why? The inner scientist in me knows that some materials will absorb more moisture than others and thus have a larger change in relative weight.

I'm no long time reloader but I've been reading a lot and many folks and manufacturers talk about setting up a powder measure system and methods to easily swap it in and out without having to recalibrate. That scares me a bit when I read the implication of a tenth of a grain of powder in cartridges like the 40 S&W.

I found this article (Tip #7) which is a good read but not a whole lot of consistent discussion on the topic.

http://www.uniquetek.com/site/696296/page/217691

Anyone else out there let the problem of moisture content in your powder and the affect on the weight bother them?

 

[mikld]

I once lived in So. CA where it often got pretty dry (low humidity), and now live in rainy So. Oregon about 1/2 mile from the ocean. In my reloading I haven't had a problem with humidity/powder weights that are significant. One reason is I very rarely approach maximum loads. Another thought (and this isn't scientific, just a thought) is the stuff in the powder that makes it burn will be just "diluted" or less concentrated with a little water (humidity) in the powder. But I also believe the difference will not be significant. I haven't reloaded in the desert so my findings/thoughts aren't a good cross section of humidity vs powder burn...

Couldn't connect with your link.

 

[SMSgt]

No. I keep it sealed in the original container when not in use and don't leave it in the powder dropper when not loading.

 

[smokindog]

Weird!!! Got to

UniqueTek.com - Products for Shooting, Reloading and Competitive Marksmen

and click "free tips files" on the left!

I once lived in So. CA where it often got pretty dry (low humidity), and now live in rainy So. Oregon about 1/2 mile from the ocean. In my reloading I haven't had a problem with humidity/powder weights that are significant. One reason is I very rarely approach maximum loads. Another thought (and this isn't scientific, just a thought) is the stuff in the powder that makes it burn will be just "diluted" or less concentrated with a little water (humidity) in the powder. But I also believe the difference will not be significant. I haven't reloaded in the desert so my findings/thoughts aren't a good cross section of humidity vs powder burn...

Couldn't connect with your link.

 

[OKFC05]

Your first link does not work.

If you follow SAAMI standards for powder and ammunition storage, there should be no problem. See the SAAMI website for details.

If a tenth of a grain variation in your load is dangerous, use another load. That is ridiculous. .40 S&W is just another high pressure round, and nobody says you have to load it at max.

Of all the things I keep track of in reloading, the exact hyumidity in the environment that is good enough for me to be comfortable is not even on the list. Any place OK for me is fine for the powder. And if you want to play the science card, I'm a no-kidding physics professor.

P.S. Military ammo sits in non-environmentally controlled bunkers for years.
Strongly suggest getting some good reloading manuals and reading them carefully, not using the "truth of conjecture on the internet."

 

[smokindog]

So the tenth of a gram was kind of tongue and cheek. I have read plenty and I'm pretty meticulous and well versed in the sciences.

There really is very little concrete information I've found about absorption properties of powder and with many products, there can be serious effects. If you're a serious baker, you worry about altitude and humidity when you measure things because baking is more chemistry than cooking.

Not trying to be a wise ... and not looking for admonishing responses. I'm looking for serious input to the effects of humidity and powder measure. If the answer is really there is none, that's great! We have fairly significant shifts in humidity and I'm trying to understand if anyone has noticed that being an impact on how they weigh/measure powder.

Your first link does not work.

If you follow SAAMI standards for powder and ammunition storage, there should be no problem. See the SAAMI website for details.

If a tenth of a grain variation in your load is dangerous, use another load. That is ridiculous. .40 S&W is just another high pressure round, and nobody says you have to load it at max.

Of all the things I keep track of in reloading, the exact hyumidity in the environment that is good enough for me to be comfortable is not even on the list. Any place OK for me is fine for the powder. And if you want to play the science card, I'm a no-kidding physics professor.

P.S. Military ammo sits in non-environmentally controlled bunkers for years.
Strongly suggest getting some good reloading manuals and reading them carefully, not using the "truth of conjecture on the internet."

 

[OKFC05]

OK, here's an answer that's as serious as a heart attack.

The weights given in the manuals are for the temp and humidity that existed in the factory for that day, and they don't tell you what those conditions were. Furthermore-and this is FAR more important--they don't tell you what powder batch was used, and you probably never could get it anyway. So every time you change your powder batch, it is vital to use a good scale to calibrate your volumetric powder measure, and then to run the load with the new batch of powder over the chronograph to see what speed it produces. I have been loading since 1973, and have found some batches of powder that were WAY different than the charts, and some that were very close. I have never found the normal ambient temp or humidity in my home to have any significant effect on powder, and I have lived in KY, IL, MD, and WA state. Even the sticky hot spells in MD still produced the same loads.

I have mentored many new reloaders, and sometimes they will stray from the recommended checklist and have problems. One in particular happened to get a particularly mild batch of HP38 to start, and as luck would have it, his next batch was unusually hot, and he did not start over to recalibrate and chrono check. Yep, he started blowing out cases, and sheer luck he did not blow a gun.
First question I asked was "Did you buy a new batch of powder?" Density varies from batch to batch.

The manuals are good starting points, but a good scale is an absolute necessity and a chronograph will keep you honest.

Some things involving reloading are not so important, and some things will hurt you.

 

[rwsmith]

In other words......

The weights given in the manuals are for the temp and humidity that existed in the factory for that day, and they don't tell you what those conditions were. Furthermore-and this is FAR more important--they don't tell you what powder batch was used, and you probably never could get it anyway. So every time you change your powder batch, it is vital to use a good scale to calibrate your volumetric powder measure, and then to run the load with the new batch of powder over the chronograph to see what speed it produces. I have been loading since 1973, and have found some batches of powder that were WAY different than the charts, and some that were very close. I have never found the normal ambient temp or humidity in my home to have any significant effect on powder, and I have lived in KY, IL, MD, and WA state. Even the sticky hot spells in MD still produced the same loads.

I have mentored many new reloaders, and sometimes they will stray from the recommended checklist and have problems. One in particular happened to get a particularly mild batch of HP38 to start, and as luck would have it, his next batch was unusually hot, and he did not start over to recalibrate and chrono check. Yep, he started blowing out cases, and sheer luck he did not blow a gun.
First question I asked was "Did you buy a new batch of powder?" Density varies from batch to batch.

The manuals are good starting points, but a good scale is an absolute necessity and a chronograph will keep you honest.

Some things involving reloading are not so important, and some things will hurt you.

Any time you change components, it's up to you to back off and work a load up again. I think this also pertains to a new lot of powder.

 

[Harrison]

Benchrest shooters know that the weight/volume ratio of powder can change with the ambient temperature and humidity and they compensate for it during a match. The also recognize that the burn rate and density of a particular powder, say VV133, can change enough from lot# to lot # to affect accuracy and charge amount. If you are shooting mid-range loads plinking away at targets, or loading for minute of deer accuracy these changes probably do not make much difference. If you are loading for maximum possible accuracy and/or maximum velocity, these changes make a whole lot of difference.

 

[MichiganScott]

Any time you change components, it's up to you to back off and work a load up again. I think this also pertains to a new lot of powder.

This is the reason I've started buying my powder in 8lb. jugs. With some magnum rifle loads, you end up burning almost 1/4 of a pound just verifying your data.

 

[H Richard]

One of the reasons I store my powder in the original can and not in a powder measure, and I turn the adjustment stem out all the way to force me to readjust my load every time I add powder to my measure. My powder is stored in my loading room and that is in a cool dry basement with the humidity controlled reasonably well around 45%. When it comes to rifle loads, I weigh every load, I don't throw by volume.

 

[rwsmith]

Another problem with this shortage...

This is the reason I've started buying my powder in 8lb. jugs. With some magnum rifle loads, you end up burning almost 1/4 of a pound just verifying your data.

I'm in a constant state of testing loads because I use whatever components I have at the time.

 

[Jellybean]

Exposing your powder to an open atmosphere will allow it to absorb mositure, or lose it depending on the relative humidity. The mositure level of powders are pretty well controlled from the factory and it is best advised to keep them in their factory containers while not being used.

From what I have read the problem isn't with moisture changing the weight per volume, which may affect how a powder flows in a measure, it's with the powder getting too dry, which increases pressures.

There are some very good reloading manuals out there, as far as reloading manuals go, but you will have to pretty much buy every one ever printed to get the kind of information you are after. Look for a copy of "Principles and Practice of Loading Ammunition" by Earl Naramore, it is out of print and is somewhat dated but everything in it pretty much deals with "modern" ammunition. If you decide to go the manual route Lapua/Vihtavuori and Lyman would be my first and second choices.