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Interesting video on reloading in different humidity conditions

Not sure why folks are surprised by this, but it may be that the advent of the internet isn't helping refine the education process (and instead it is diluting it).

It probably should be a part of basic reloading manuals, but because a few of the popular ones skip the concept many folks don't hear it up front when they are starting out.

The Norma manual has a section on the concept, but I can't think of another popular modern one that does and that is probably why this seems like a surprise to many.

The powder/water content relationship has been well understood since long before any of the smokeless powder we are using ever existed. The effect water content of propellant has on speed/pressure is independent of the temperature and pressure of the loading day or shooting day even if the altitude is very high and well below freezing (think aircraft).

Some forms of artillery are loaded with on-demand charges from powder magazines. Their powder was subject to all sorts of conditions and weather changes. Some very bright folks picked up on the concept that first salvo hits were more likely if they factored for the water content of the powder.

There are some beautifully written papers on the topic that are very very old, but you won't see them on the internet. By the time your grandfathers were born, the concept was well understood and each new propellent was evaluated for the sensitivity if used in mil ammo.

If you are concerned about keeping the muzzle velocity as predictable as possible on preloaded ammo, then you have to pay attention to the powder water content.
 
Interesting you would post this today. I was looking over some data from 2021 when I got my first 6 BRA this morning. I was using an older jug of H4895 I had stored in my workshop for a few years and had been into several times. I was seeing way lower velocity than others were reporting. A Facebook post received the suggestion to dry the powder in a food dehydrator for a couple of hours. I ran a 30gr sample in a weigh boat from my chargemaster along with a couple of pounds of powder in tin foil pouches and noted an almost 1.5% weight loss from the dehydration. Temperature was low enough I was not concerned with degrading any of the chemistry of the powder but I am sure some of the solvent "ether smell was driven off with the 1.5% water vapor.
I repeated the ladder with the dried powder and saw about a 200 fps increase from the previous days data. (2785 to 2980fps) for 30.0 gr H4895 with a 105 Berger. (26" barrel CCI450 Lapua brass 1x fired)

Since then I have moved all my powder into MTM totes with rubber gaskets and desiccant bags in them. I also moved storage into my office instead of an uncontrolled workshop attached to the garage. Much more consistent results since then.
 
I repeated the ladder with the dried powder and saw about a 200 fps increase from the previous days data. (2785 to 2980fps) for 30.0 gr H4895 with a 105 Berger. (26" barrel CCI450 Lapua brass 1x fired)
That's remarkable. I remember hearing that powder could absorb moisture. Some guy posted that a scale pan of powder left out would gain weight. I tried it, and the pan weight didn't change in my environment.

I'm in the Phoenix area where it's generally dry, but I'll have to be mindful of loading on high humidity days.
 
The question is not whether a significant change in the moisture content of a given Lot# of powder can affect velocity, it obviously can. The real question is to what extent the average reloader is experiencing drastic changes in their powder moisture content from opening a powder keg to load rounds at various times during the year. What I can tell you is that I store my powder at room temp in an air conditioned/heated living area and have never observed velocity swings outside the typical ES observed for loaded rounds that could be attributed to a major change in the moisture content of a given Lot# of powder. Never. And believe me, I would have noticed immediately if it were to have happened. I have no idea how those that have actually experienced this problem are handling their powders, but it doesn't take much to prevent this issue from occuring in any significant way.
 
While I've always been aware of this issue, I never paid much attention as the room where I keep my powders is a controlled environment and pretty consistent, though the normal climate here in my part of Arizona can be very, very dry. About a year and a half ago I decided to add the powder moisture content data to my tracking data sheet, so now I take that moisture content measurement each time I start to load up. So far, it's all been pretty consistent with not much lowering of moisture contents from first opening a bottle of powder (might vary as much as 1 percentage point).

A couple old jugs of powder that's been sitting around did have lower moisture than where it should have been, so I dropped a Boveda humidity control pack in them to bring the moisture up. That's been some time ago, and one of these days I'll have to load some of this up and see if the added moisture will give me the same results as I compare it to the old data I've saved. When I do, I'll post my results.
 
Here in the Corn belt - it is sauna like 90% humidity and 100 degrees in the summer and bone dry less than 20% in the winters and wildly swinging in between those extremes daily through the years. Until 2021 I knew it was problematic but had never put a number to it. I had a jug of H414 I have been using for .243 coyote loads for about a decade too and thought it was degrading but after drying it out the velocities came back up. as Ned says - an ounce of prevention. Keep the jugs well sealed in a controlled environment and it will not be noticeable. Leave some in you powder measure hopper in your open garage for a few days and come back to it and see if you can match the same velocity as before...
 
When loading at the range, you can see results of drying powder pretty darn fast.
Exposed to the dry air in the desert SW, a 30gr charge of 133 will lose .2gr in 15 min.
CW
Yeah, here in the desert it can be a day with humidity at 10 - 15%, then a monsoon storm passes through and the humidity suddenly jumps to 80 - 90%. Such extremes can have a significant effect on the powder for the time one is doing their loading out in the open at the range. :eek:
 
So based on what mulligan and straightshooter said, I have a incredibly novice and I’m guessing silly question. Once the powder is loaded in the round sealed with a bullet, it’s an airtight space that the powder is no longer affected by humidity? So of if you load at home in a dry room and go outside to a super humid match day, as opposed to loading at the match, you are only dealing with the effects of humidity on your bullet in air? Or is your powder somehow still susceptible to the humidity. Try not to laugh at this question.
 
So based on what mulligan and straightshooter said, I have a incredibly novice and I’m guessing silly question. Once the powder is loaded in the round sealed with a bullet, it’s an airtight space that the powder is no longer affected by humidity? So of if you load at home in a dry room and go outside to a super humid match day, as opposed to loading at the match, you are only dealing with the effects of humidity on your bullet in air? Or is your powder somehow still susceptible to the humidity. Try not to laugh at this question.
I have not tested that, however at the risk of looking like an idiot, I will venture a guess that I am not a good enough shooter to even see the difference on target.
Exposing powder to single digit RH and 90 degree heat will make H4350 burn like varget.

I am running an experiment at this time.
I just exposed a single charge of N-133, N-540, and 8208XBR to current outside conditions here in Western Colorado. All lost .25gr of weight in 45 min. with most of that moisture loss in the first 15 minutes.

CW
 
So based on what mulligan and straightshooter said, I have a incredibly novice and I’m guessing silly question. Once the powder is loaded in the round sealed with a bullet, it’s an airtight space that the powder is no longer affected by humidity? So of if you load at home in a dry room and go outside to a super humid match day, as opposed to loading at the match, you are only dealing with the effects of humidity on your bullet in air? Or is your powder somehow still susceptible to the humidity. Try not to laugh at this question.
An excellent question.

Ammo assembled without a sealant at the neck or primer can change with storage conditions.

A strong difference in humidity outside the ammo can be driven by temperature or pressure cycles to accelerate the change rate.

Mil spec ammo is sealed at both the neck and primer, and this is one of many reasons.

For unsealed ammo, loading as near to 50% RH as possible and storing and transporting very carefully can keep that ammo nearer to nominal when the time comes.
 


Don’t know if this guy is a member here, but does mention accurate shooter so I am assuming he is. But I thought this was a very interesting video he made. Much bigger swings than I imagined.
other resources:


from 2008:
 
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So based on what mulligan and straightshooter said, I have a incredibly novice and I’m guessing silly question. Once the powder is loaded in the round sealed with a bullet, it’s an airtight space that the powder is no longer affected by humidity? So of if you load at home in a dry room and go outside to a super humid match day, as opposed to loading at the match, you are only dealing with the effects of humidity on your bullet in air? Or is your powder somehow still susceptible to the humidity. Try not to laugh at this question.
That's certainly NOT a "silly question".

As RegionRat pointed out, unless some kind of sealant is used around the primer and in the neck, the interior of a loaded cartridge is not an "airtight space". Heating up the case will cause the air inside the cartridge to expand causing some of it to leak out (slowly) and cooling of the cartridge will do the opposite where outside air will be drawn in (slowly). How fast air will be pushed out or drawn in will depend on the pressure difference between the interior and exterior. How much will be pushed out or drawn in will depend on both that pressure difference along with the time period. Low pressure difference will take longer for much to happen than higher pressure. Depending on how long the cartridge has been loaded and what temperature changes its subjected to (and don't forget elevation changes, like watching a bag of potato chips expand as one drives to a higher elevation), these changes that might occur repeatedly over time will effect the moisture content inside the cartridge. But, to have a significant effect there has to be some substantial changes occurring over time. Big changes in elevation, like driving from 500 ft at a low desert level to 7,000 ft would certainly cause the case to loose some air (assuming a constant temperature); though a lowering temperature as one ascends can have some offsetting effect. While these effects happen, there very few shooters that ever have any need to think about it. As far as loading at the range, one only needs to be concerned if the humidity is extreme one way or the other or the powder sits exposed for a long period of time.

Anyway . . . this is my take on your question.
 
Hmmmmmmm. Being able to manipulate the moisture content to get a better case fill ratio at safe pressures without compression.
 
So based on what mulligan and straightshooter said, I have a incredibly novice and I’m guessing silly question. Once the powder is loaded in the round sealed with a bullet, it’s an airtight space that the powder is no longer affected by humidity? So of if you load at home in a dry room and go outside to a super humid match day, as opposed to loading at the match, you are only dealing with the effects of humidity on your bullet in air? Or is your powder somehow still susceptible to the humidity. Try not to laugh at this question.
There are at least a couple ways I can think of by which varying the moisture content of powder could affect velocity. The first would be that you're actually measuring out more "combustible material" when throwing a given charge weight if the moisture content is low because the weight component due to water is lessened. In theory, the water content of the powder could also affect the burn rate. Of these, I think the first is likely what is happening when reloaders observe velocity changes due to altered moisture content. The powder becomes "lighter" on a volume basis because the water content is lower. Thus, a given charge weight from a Lot# of powder with low moisture content actually contains more combustible material than the same charge weight as measured out from a Lot# of powder with higher water content.

The two ways these events would affect velocity would be A) the "effective" charge weight varies between individual loaded rounds within a single loading session/day more than would be expected based on measured charge weight, and B) the "effective" charge weight varies over time. In example A), the moisture content would have to be changing pretty fast, as was described when loading at a match in a very dry/humid climate. In example B), one might end up with very uniform charge weight in a batch of ammunition loaded on a single day, but the charge weight wouldn't be the same as rounds loaded much earlier/later when the moisture content was different. The problem in this scenario would be that although you might obtain very uniform charge weight within a single loading session, it could change over time, potentially throwing the load out of tune.
 
Of these, I think the first is likely what is happening when reloaders observe velocity changes due to altered moisture content.
Water content changes both parameters, the density as well as the combustion energy per grain.

So, careful charge weight management without water content discipline will still result in velocity changes.

Many reports of batch to batch "burn rate problems" with powder were the result of a lack of water content discipline. When the suspect powders were put back within normal humidity, their "burn rate" returned to "normal", and all of those misinterpretations came from "weighed charges".
 

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