How does humidity affect powder? A new experiment

[mc10]

The humidity of your powder can have an impact on your load's performance and consistency. But there's little in the way of actual public data about it. I wanted to collect the highest quality data I could, so I sent 120 rounds downrange to measure just that.

I tested H4350 at five different humidity levels and measured how moisture affects the velocity and pressure of a load (spoiler: it's significant). I then isolated and measured exactly how much of that effect is due to the change in weight of the powder vs. the change in burn rate.

Let me know what you think!

How does humidity affect powder?

You may have heard about a relationship between humidity and bullet velocity either in a book, on a reloading forum, or from a crusty benchrest shooter right after saying they get better ES/SD&#821…

chronoplotter.com

 

[davidjoe]

You have extra H4350 on hand, do ya?

 

[RegionRat]

Very nice work Michael.

I ran tests back in the 80's and didn't understand the fuss till we complied the results. Your results mirror the ones from a full up Fortune 500 sized lab, well done for a hobbyist.

The only disadvantage you had was the lack of large "glove boxes" where all the work was done to control the Rh for those samples. You obviously worked quickly enough that the extreme samples didn't change much where I could take all the time I needed cause the inside of those enclosures was constant.

I have been loading with a hygrometer at home since the 80's as a result. I live where the winds carry a very steady Rh from the ocean but when the desert winds (Santa Ana) come up, we can get very dry and it happens quickly.

I learned how to factor for Rh long ago and it bears repeating it with your article that serious loaders should at least monitor Rh and I would say factor for it when necessary. Your velocity change could have easily come from typical Rh swings in the Northeast.

Mil-Spec rounds are often sealed at the primer and neck for several reasons, but in this discussion it would make the time constants very long in terms of how long it would take for say ammo loaded in a controlled Rh factory to dry or saturate due to external conditions.

I later measured samples of propellants stored in container conditions in deserts or high humidity, and was happy to see they were unchanged after decades. Unsealed ammo was a different story. It would be difficult to estimate the time constants for storage conditions to affect ammo without sealants. That would be worth a look but would also require lots of money and time.

At another point in my career I was tasked with several committees including the packaging specs. The relevance today was I learned how interesting different seals and polymers worked with respect to being water barriers for example.

I can tell you your plastic bags didn't accomplish anything if they were Polyethylene which allows humidity to pass easily and relatively quickly. If you want to bag something to keep humidity out you have to use barrier films like Aclar for example. You Mason jars work fine, but many common household plastics are no good for humidity because they are made of inexpensive polyethylene which passes water like a sieve.

Thanks for posting you work. It should help remind folks to at least take humidity serious enough to go buy a decent hygrometer and sit it in their reloading work area to watch the levels. Well Done.

 

[Jager]

Thanks for the deep dive into an area of interior ballistics that has largely been ignored, for much too long.

I don't have any answers. Only a few thoughts/questions....

Yes, the nitrocellulose that forms the basis of all smokeless powders is hygroscopic. But beyond the nitroglycerine that is also added to double-base powders, smokeless powders are also coated with various substances, for various reasons - and that raises the question of do those coatings inhibit (or enhance) a powder's propensity to absorb moisture? And that question then leads to do powder brands/types vary in how readily they absorb moisture?

Another question is the degree to which the factory canisters that powder comes in are air tight? Containers today are pretty much all plastic. But in the past we've seen both metal (old Dupont powders) and paper (old Hercules powders) containers. Which material is best? And when we open up a virgin canister of our favorite propellant, tear off the thin, flimsy paper seal from over the opening, pour some powder from it into our hopper, then screw the plastic cap back on... how "airtight" is the bottle compared to a virgin bottle with the seal still intact?

I suspect most of us kinda figure that once we've loaded a round, it's reasonably airtight. But is it?

Two quick thoughts on your test methodology.... it makes perfect sense to use extremes of relative humidity... as that is more likely to reveal statistically significant variance. But it begs the question of how much RH variation most of us actually see?

And, lastly, relative humidity changes as temperature changes. So using it, alone, to track moisture in the air becomes a little bit like whack-a-mole. Dew point is probably a better measure for what we're trying to understand here.

Thanks again for the most excellent work. I hope you (and Bryan Litz and a bunch of others) continue to explore this mostly dark corner of our handloading world.

 

[CharlieNC]

Nice work, it certainly required a lot of time and careful effort. As noted in the previous post, the RH does not measure the actual amount of moisture in the air as shown in the chart below. Not nitpicking your good work, just for reference since RH might be misleading if you expanded the effort at different temperature.

 

[RegionRat]

I suspect most of us kinda figure that once we've loaded a round, it's reasonably airtight. But is it?

I can field this one. The answer is, yes and no... Non sealed ammo will "leak" but the answer means that the time constant is known to be very slow. So if for example you load ammo in "good" conditions and take a trip to "bad" ones, the ammo will take a long time to change.

How long was the question I posed above. It would take lots of time and effort to create a few examples and run exposure tests. I can tell you ammo that got baked in shipping containers in the desert, gets dried out. I can't tell you how fast.

But it begs the question of how much RH variation most of us actually see?

The Rh of where you live isn't hard to grasp, and you can see the scales on those plots. I know mine can stay very close to 50% unless we get Santa Anas. We don't run air conditioners and rarely run heat, so those can affect you. I would always advise buying a hygrometer.

And, lastly, relative humidity changes as temperature changes. So using it, alone, to track moisture in the air becomes a little bit like whack-a-mole. Dew point is probably a better measure for what we're trying to understand here.

No. Dew point is important, but not what matters unless you are loading black powder outside in your deer stand in fog. Get an Rh meter and keep an eye on it.

 

[mc10]

Very nice work Michael.

I ran tests back in the 80's and didn't understand the fuss till we complied the results. Your results mirror the ones from a full up Fortune 500 sized lab, well done for a hobbyist.

The only disadvantage you had was the lack of large "glove boxes" where all the work was done to control the Rh for those samples. You obviously worked quickly enough that the extreme samples didn't change much where I could take all the time I needed cause the inside of those enclosures was constant.

I have been loading with a hygrometer at home since the 80's as a result. I live where the winds carry a very steady Rh from the ocean but when the desert winds (Santa Ana) come up, we can get very dry and it happens quickly.

I learned how to factor for Rh long ago and it bears repeating it with your article that serious loaders should at least monitor Rh and I would say factor for it when necessary. Your velocity change could have easily come from typical Rh swings in the Northeast.

Mil-Spec rounds are often sealed at the primer and neck for several reasons, but in this discussion it would make the time constants very long in terms of how long it would take for say ammo loaded in a controlled Rh factory to dry or saturate due to external conditions.

I later measured samples of propellants stored in container conditions in deserts or high humidity, and was happy to see they were unchanged after decades. Unsealed ammo was a different story. It would be difficult to estimate the time constants for storage conditions to affect ammo without sealants. That would be worth a look but would also require lots of money and time.

At another point in my career I was tasked with several committees including the packaging specs. The relevance today was I learned how interesting different seals and polymers worked with respect to being water barriers for example.

I can tell you your plastic bags didn't accomplish anything if they were Polyethylene which allows humidity to pass easily and relatively quickly. If you want to bag something to keep humidity out you have to use barrier films like Aclar for example. You Mason jars work fine, but many common household plastics are no good for humidity because they are made of inexpensive polyethylene which passes water like a sieve.

Thanks for posting you work. It should help remind folks to at least take humidity serious enough to go buy a decent hygrometer and sit it in their reloading work area to watch the levels. Well Done.

I appreciate the kind words! It sounds like you had some fun equipment you got to use!

The Norma manual article actually tested % RH effect on unsealed loaded ammo. It for sure depends on the ammo you're testing, internal and external humidities, but they found their ammo took about one year to equalize with its environment.



That's good to know that Ziploc bags aren't effective at preventing moisture transfer, I'll scrap them in the next test.

 

[RegionRat]

Nice work, it certainly required a lot of time and careful effort. As noted in the previous post, the RH does not measure the actual amount of moisture in the air as shown in the chart below. Not nitpicking your good work, just for reference since RH might be misleading if you expanded the effort at different temperature.

View attachment 1274413

@CharlieNC , If you are loading in a really hot or really cold place, then you have lots of other things to account for as you point out. But, that said, there are even other factors in terms of how the powder was at the beginning of a loading session versus exposure to a "shock" condition that matter too.

If for example, you took powder from a cold place at low Rh and loaded in a lab with normal humidity, as some factories thought was okay, then there is another time constant to consider in terms of how fast does the powder gain water and what the powder column shape looks like in terms of exposure. We started specifying the propellant storage conditions and included enough time for them to stabilize to the loading rooms.

The poster gave things time to saturate or nearly saturate within one time constant. we ran out past 10 time constants to be thorough but five would have been enough. (If you suspect your powder is very wet or very dry, try and open the can in the condition where it is to be loaded for 48 hours or more before you load.)

But to your question, we can only measure weights and weight changes in the propellants in a practical sense. Temperature, and humidity are easy enough since there is nothing we can do about the pressure where we live but we can try and do something with Rh and temp.

 

[PigButtons]

Scientific method at work. Great post, thanks.

 

[RegionRat]

It sounds like you had some fun equipment you got to use!

https://en.wikipedia.org/wiki/Hughes_Aircraft_Company

https://en.wikipedia.org/wiki/Chain_gun

You get the picture...

 

[mc10]

Thanks for the deep dive into an area of interior ballistics that has largely been ignored, for much too long.

I don't have any answers. Only a few thoughts/questions....

Yes, the nitrocellulose that forms the basis of all smokeless powders is hygroscopic. But beyond the nitroglycerine that is also added to double-base powders, smokeless powders are also coated with various substances, for various reasons - and that raises the question of do those coatings inhibit (or enhance) a powder's propensity to absorb moisture? And that question then leads to do powder brands/types vary in how readily they absorb moisture?

Absolutely good questions, I'd suspect yes for both. It was a ton of work to set up, but hopefully down the line I can repeat testing for other popular powders.

Double base powders theoretically should be less sensitive to humidity changes, but earlier today someone brought up a fascinating point - When double base powder is desiccated the nitroglycerin content may actually be extracted to the surface of the kernel, which ends up causing an initial pressure spike. Would be curious to measure it.

Another question is the degree to which the factory canisters that powder comes in are air tight? Containers today are pretty much all plastic. But in the past we've seen both metal (old Dupont powders) and paper (old Hercules powders) containers. Which material is best? And when we open up a virgin canister of our favorite propellant, tear off the thin, flimsy paper seal from over the opening, pour some powder from it into our hopper, then screw the plastic cap back on... how "airtight" is the bottle compared to a virgin bottle with the seal still intact?

Maybe Hodgdon or another manufacturer would be willing to answer this over a call. My understanding is that new powder jugs should be sealed, but it's possible they're not 100% for cost or safety reasons.

I suspect most of us kinda figure that once we've loaded a round, it's reasonably airtight. But is it?

See Norma article posted above

Two quick thoughts on your test methodology.... it makes perfect sense to use extremes of relative humidity... as that is more likely to reveal statistically significant variance. But it begs the question of how much RH variation most of us actually see?

Much of the country (and around the world) certainly doesn't see such wild humidity swings throughout the year. It's definitely significant in the Northeast from winter-summer, at least, but I haven't properly measured it aside from glances at my thermostat. I set up a Kestrel DROP in my reloading room I'll keep tabs on over the year.

And, lastly, relative humidity changes as temperature changes. So using it, alone, to track moisture in the air becomes a little bit like whack-a-mole. Dew point is probably a better measure for what we're trying to understand here.

Good point!

 

[CharlieNC]

@CharlieNC , If you are loading in a really hot or really cold place, then you have lots of other things to account for as you point out. But, that said, there are even other factors in terms of how the powder was at the beginning of a loading session versus exposure to a "shock" condition that matter too.

If for example, you took powder from a cold place at low Rh and loaded in a lab with normal humidity, as some factories thought was okay, then there is another time constant to consider in terms of how fast does the powder gain water and what the powder column shape looks like in terms of exposure. We started specifying the propellant storage conditions and included enough time for them to stabilize to the loading rooms.

The poster gave things time to saturate or nearly saturate within one time constant. we ran out past 10 time constants to be thorough but five would have been enough. (If you suspect your powder is very wet or very dry, try and open the can in the condition where it is to be loaded for 48 hours or more before you load.)

But to your question, we can only measure weights and weight changes in the propellants in a practical sense. Temperature, and humidity are easy enough since there is nothing we can do about the pressure where we live but we can try and do something with Rh and temp.

I don't have an issue since I load inside in a reasonably controlled environment. But I often see guys loading outside at the range over the course of hours, and the temperature/humidity vary wildly here in Charlotte. Many possibilities to introduce and accumulate moisture variability.

 

[Jager]

I set up a Kestrel DROP in my reloading room I'll keep tabs on over the year.

I, too, have been using Kestrel DROP's to monitor environmentals in my powder closet and in the upstairs bedroom where I do my handloading.

And this past spring I added a new column - "Dew Point" - in my handload log to track moisture in the air during the period in which any powder is exposed to the air... i.e. out of its factory canister and sitting in a hopper or in cases in a loading tray. And although I've long been pretty relaxed about leaving powder sitting in a hopper for a few days - my biggest worry being that it might etch the plastic of the hopper if left there too long - I now try and minimize the time powder is "exposed."

Again, your work here is very significant and I will be watching your efforts with keen interest. And ChronoPlotter is a super program for anyone running a chrono!

 

[mc10]

I, too, have been using Kestrel DROP's to monitor environmentals in my powder closet and in the upstairs bedroom where I do my handloading.

And this past spring I added a new column - "Dew Point" - in my handload log to track moisture in the air during the period in which any powder is exposed to the air... i.e. out of its factory canister and sitting in a hopper or in cases in a loading tray. And although I've long been pretty relaxed about leaving powder sitting in a hopper for a few days - my biggest worry being that it might etch the plastic of the hopper if left there too long - I now try and minimize the time powder is "exposed."

Again, your work here is very significant and I will be watching your efforts with keen interest. And ChronoPlotter is a super program for anyone running a chrono!

I appreciate it! I'm glad it's useful, it took a lot of work to transpire

 

[RegionRat]

I don't have an issue since I load inside in a reasonably controlled environment. But I often see guys loading outside at the range over the course of hours, and the temperature/humidity vary wildly here in Charlotte. Many possibilities to introduce and accumulate moisture variability.

Yes, if you know you are loading where your powder is getting a shock in humidity or temperature, you should expect trouble. The tree stand example I gave was the obvious one, where you are vulnerable when muzzle loading in the field.

Some of our field labs had a problem, but I was able to justify air handlers for controls as a result of showing the management there was a risk. Air handlers are not cheap, not to mention the grief I got when I slammed some ammo plants with the new specs. Some folks invoke their egos, but some backed off when they saw the data. I invited some of the naysayers to join us on a two way target range and told them they would go up front if they kept arguing.... Eventually cooler heads prevailed and ammo labs are now typically controlled by contracts if not by specs.

 

[Doom]

I was impressed by the detail you put into the experiment. Good work, However, I would like to elaborate on one item that has been brought up in Post #5 by CharlieNC. As implied by it's name Relative Humidity is a relative term. It is actually calculated from dew point and dry bulb temperature. The amount of moisture, typically referred to as specific humidity (Lb H2O /#LB of dry air), varies with dew point temperature. Your test was run around humidities corresponding to around room temperature or storage temperature, lets assume 70F. However, if the storage were done at 45F ambient dry bulb and 66% relative humidity, the air holds considerably less moisture, 0.0014 Lb H2O /#LB of dry air as opposed to the 70F case where it holds .0036 Lb H2O /#LB of dry air. This environment would actually dry the powder stored at 70F and 68%RH.

 

[mc10]

I was impressed by the detail you put into the experiment. Good work, However, I would like to elaborate on one item that has been brought up in Post #5 by CharlieNC. As implied by it's name Relative Humidity is a relative term. It is actually calculated from dew point and dry bulb temperature. The amount of moisture, typically referred to as specific humidity (Lb H2O /#LB of dry air), varies with dew point temperature. Your test was run around humidities corresponding to around room temperature or storage temperature, lets assume 70F. However, if the storage were done at 45F ambient dry bulb and 66% relative humidity, the air holds considerably less moisture, 0.0014 Lb H2O /#LB of dry air as opposed to the 70F case where it holds .0036 Lb H2O /#LB of dry air. This environment would actually dry the powder stored at 70F and 68%RH.

Thanks for the explanation, that makes a lot of sense. For future experiments then, would it be sufficient to report/measure % RH but accompany it with a temperature reading? Or does it make more sense to measure one of these different metrics instead?

 

[RegionRat]

@mc10 , the best goal is to try and keep your powder at a baseline. Room temp and 50% Rh, or as close to that as possible.

It isn't enough to know the temp and Rh at the moment, but you would need to also know that the powder was most recently normalized prior to your loading session. So if you know the powder is very hot or cold or very wet or dry where you store it, give it two days to normalize where you load.

I live in a desert, but near the ocean. I keep both a humidifier and a dehumidifier in the house. Our humidity can go up or down depending on the seasons, so if it matters to you then begin by observing as soon as you can. The weather apps and internet publish all you need to know and then some, but it is very easy to place a hygrometer in your storage and loading area.

Many target games offer unlimited sighters, others do not. Hunting at a distant place compared to where you live for example may mean you need to take some test shots when you arrive. This isn't important to many folks, but it is to others. (Snipers, soldiers, tanks, artillery, battleships, etc., don't get to dictate terms for example, they have to count on their velocity.)

The farther away from standard conditions your powder was stored, the more complex the compensation will be if you have to load it that way. The same goes for the loading session.

It is far less complex to keep things in household room conditions and start watching the Rh where you store your powder, than it is to compensate for extreme conditions. The main takeaway is that Rh inside your house and in your local weather can and does go out of bounds, enough to affect your average velocity and potentially enough to take a narrow node out of tune.