How does humidity affect powder? A new experiment

mc10

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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!

 
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6.5SH

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That is a great article, thanks for taking the time and effort to test all that and document it. (y)
 
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spife7980

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I love a good graph, excellent work. Backs up what everyone has always said but with some decent data... though I never imagined that it would effect it to that extent! 200 fps is crazy
1629396864114.png
 

D_TROS

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    Its very substantial if you live on one of the extremes for humidity. I live in semi-aid desert. I will notice a 5% diff in powder from opening a 8lb keg to the powder at the end.

    (I literally did a ton of testing from weighing both and counting the actual kernals and 5% was the diff. That was equal to roughly 1.5 gr of powder for this particular powder.)

    When I first started using 8 lbs jugs, it was substantial enough to make my rifle unsafe blowing primers when I thought I was well under pressure. Lucky I kept lowering the charge as the keg emptied as at matches I noticed the velocity waas above what it should be.

    Please please be careful!!


    GL
    DT
     

    Punkur67

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    What are thoughts on storing powder in a safe with a de-humidification rod?
     

    mc10

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    Its very substantial if you live on one of the extremes for humidity. I live in semi-aid desert. I will notice a 5% diff in powder from opening a 8lb keg to the powder at the end.

    (I literally did a ton of testing from weighing both and counting the actual kernals and 5% was the diff. That was equal to roughly 1.5 gr of powder for this particular powder.)

    When I first started using 8 lbs jugs, it was substantial enough to make my rifle unsafe blowing primers when I thought I was well under pressure. Lucky I kept lowering the charge as the keg emptied as at matches I noticed the velocity waas above what it should be.

    Please please be careful!!


    GL
    DT
    That's a massive change! Scary if you're not expecting it
     

    samb300

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    I have seen this with an 8# jug as I don't shoot enough to go through multiple jugs a season like some shooters. My velocity slowed down and I needed to add to the charge weight to keep the same speed.

    Do we know if there is any factory seal on new jugs? The control group was 53% RH, does that mean that's what it was from the factory, or what it was in your house where it was stored?

    I tend to gravitate toward 1# containers for this reason, even if they are more expensive. The 2-way humidity packs on Amazon are very interesting though.

    I think I will measure the humidity of my basement with my Kestrel and see what it is now in summer with the AC on vs in the winter with the heat on, and maybe pick up some of those packs to test it out. Not sure how well one of those can change 1# or 8# of powder though.
     
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    mc10

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    I have seen this with an 8# jug as I don't shoot enough to go through multiple jugs a season like some shooters. My velocity slowed down and I needed to add to the charge weight to keep the same speed.

    Do we know if there is any factory seal on new jugs? The control group was 53% RH, does that mean that's what it was from the factory, or what it was in your house where it was stored?

    I tend to gravitate toward 1# containers for this reason, even if they are more expensive. The 2-way humidity packs on Amazon are very interesting though.

    I think I will measure the humidity of my basement with my Kestrel and see what it is now in summer with the AC on vs in the winter with the heat on, and maybe pick up some of those packs to test it out. Not sure how well one of those can change 1# or 8# of powder though.
    From what I understand factory new jugs are sealed and shouldn't be affected by their environment's humidity until they're first opened. At least in the experiment, I used a new/sealed jug of H4350
     
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    Mike_in_FL

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    There is an Everyday Sniper podcast with the Berger guys, Bryan and Emil talking about this. One of them said even though Berger is in AZ their ammunition line would shut down for a couple of weeks due to rain and no climate control in the building. Also, don't dry your powder in the oven, lol.
     

    greentick

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    <snip>....Each sample took about 24-48 hours to stabilize to its target humidity, which it then maintained for the remainder of the time....

    This is really useful, love this kind of reloading research. I store my powder in the house, RH stays +/- 50%, but reload in the garage. Looks like I'm safe if I pour when I start a reloading session and put anything I don't use back in the jug as soon as I'm done.
     

    Bmghunter

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    bolt action reloading on youtube did a video 4 months back testing humidity vs velocity. looks like humidity has a huge impact in that video also.
     

    whatsupdoc

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    Hodgon 8lb jugs are crap, the mouth lip is kind of ragged and many times the "seal" is not properly bonded to
    the container mouth. The container is made from HDPE so it has good moisture barrier properties
    but is a poor oxygen barrier.
    Not sure if oxygen is detrimental to smokeless powder but I would think long term it is.


    From the VihtaVuori Web Site:

    ----------------------------------------------------------------------------------------------​

    Did you know? Powder moist content​

    18.07.2018

    Variations in moisture content change the burning rate of a powder and thereby chamber pressures and muzzle velocity. The moisture content of the N100 and N300 series powders is usually around 1 %, the N500-series’ normal moisture content is 0.6 % because of the added nitroglycerine.
    So what difference does moisture content have? Here’s an example. In a test, a powder sample was dried by heating it, losing about 0.5 % of its weight. Cartridges were then loaded with the dried powder and fired using a pressure gun. Chamber pressures and muzzle velocities produced by these special cartridges were compared to those produced by cartridges loaded with untreated powder. (The powder charge and bullet were of course the same in both sets of cartridges.)
    Comparing results showed chamber pressures increased from 320 MPa to 355 MPa with the dried powder, and the muzzle velocity increased accordingly from 770 m/s to 790 m/s (2526 to 2592 fps). And note, this is only one example, of one caliber and loading. The difference might be much higher depending on the cartridge and loading combinations.
    What does this tell us? Well, it seems we need to forget the old saying “Keep your powder dry”! Instead, focus on proper powder storage, at a temperature below 20°C / 68°F and humidity between 55-65 %. Safe reloading everybody!
    ---------------------------------------------------------------------------------------------------------------------

    Their powder has a moisture content of .06% to 1% so this leads me to believe that most smokeless powder will fall
    somewhere close to that range.

    So am I understanding that 55-65% humidity will keep the moisture content between the .06% to 1% range.
     

    KZP

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    Great🤦🏼‍♂️ another thing to worry about in the reloading process…why do I do this again?

    Hope your wallet is ready. Coming soon, AMP powder drying machine. Press a button for the perfect moisture ratio. Sadly to get the proper drying code, you will have to burn up 1lb of powder during calibration.

    I'm going to deal with losing some of the velocity potential to keep it simple. At least my house RH is fairly consistent. A humidifier runs in the winter to keep it around 45% RH, so I shouldn't be too far off in summer months with AC running.
     

    308sako

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    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!

    This is a turly eye opening moment. Due to current market conditions I've been shooting some very older powders which while stored in consistent conditions, well it's the desert and humidity is scarce. So obviousily older data point simply aren't matching. Now I know why. Thank you.
     
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    6.5SH

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    Earlier this year I had experienced the mirror image, a sudden increase in velocity that wrecked accuracy and took my load into unsafe pressures.
    I had heard the comments by Litz in Frank's podcast and assumed that was what happened but did not do the extensive amount of testing @mc10 did.

    Again, fantastic work and nice to have validation. Absolutely going to try the humidor pack idea out myself.
     
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    6.5SH

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    A related tangent. While I love my Kestrel D3 and 5700, the Drops are not exactly inexpensive.

    A few items to look at for continuous monitoring of opened containers:



    Be sure to read user comments before committing to anything, there are pros and cons to all of them.

    There are very cheap units that can show current humidity, but it doesn't cost that much more to get logging to see data over time.
     

    ThePretzel

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    A pipe bomb is just powder in a sealed steel container.
    I had a roommate in college who wanted me to store 40ish pounds of powder inside my self-sealing fireproof safe. He changed his mind when I agreed so long as he called the fire department and notified them of exactly how big a bomb he was requesting I made, to properly warn them in case there was a fire anywhere in our building.

    I love a good graph, excellent work. Backs up what everyone has always said but with some decent data... though I never imagined that it would effect it to that extent! 200 fps is crazy
    I live in a very dry climate, and I know that before I started humidity stabilizing my powder I would get a 40-50 fps velocity increase from the first rounds I loaded and the last rounds I loaded that had been sitting at the top of the powder hopper for 2-3 hours drying out. That was with Varget in a BR, so small changes to powder can make a bigger difference due to the smaller charge weight.

    After humidity stabilizing my powders, my powder charge weights actually decreased noticeably for the equivalent velocity. My Dasher load for 109 Hybrids at 2875 fps is only 31.0gr of powder, because the dryer powder has more propellant when measured by weight (and has a faster burn rate). My max load in Dasher with 105's was only 32.4gr of powder at nearly 3030fps, much faster than most published data specifically because of the humidity differences. Stabilizing my powder, however, has ensured that the first and last rounds I load are the same velocity along with every round loaded in between.
     

    NodakBarbarian

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    I had a roommate in college who wanted me to store 40ish pounds of powder inside my self-sealing fireproof safe. He changed his mind when I agreed so long as he called the fire department and notified them of exactly how big a bomb he was requesting I made, to properly warn them in case there was a fire anywhere in our building.


    I live in a very dry climate, and I know that before I started humidity stabilizing my powder I would get a 40-50 fps velocity increase from the first rounds I loaded and the last rounds I loaded that had been sitting at the top of the powder hopper for 2-3 hours drying out. That was with Varget in a BR, so small changes to powder can make a bigger difference due to the smaller charge weight.

    After humidity stabilizing my powders, my powder charge weights actually decreased noticeably for the equivalent velocity. My Dasher load for 109 Hybrids at 2875 fps is only 31.0gr of powder, because the dryer powder has more propellant when measured by weight (and has a faster burn rate). My max load in Dasher with 105's was only 32.4gr of powder at nearly 3030fps, much faster than most published data specifically because of the humidity differences. Stabilizing my powder, however, has ensured that the first and last rounds I load are the same velocity along with every round loaded in between.
    How did you go about humidity stabilizing your powder?
     
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    mark5pt56

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    Wow!, so I'm in SW Florida and loaded some rounds in the garage, was about 90 with the typical humidity we have. Never knew this, and another rabbit hole
     

    Steel head

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    I have a kestrel D3, I should pull it out of my humidor and put in my powder cabinet(an old dead refrigerator) that has super sized desiccant packs in it and see how it going in there.
     

    ThePretzel

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    How did you go about humidity stabilizing your powder?
    Spread it out to dry in a large container during a week when there was no rain or snow and the dew point stayed near the local average the entire week. Mixed/stirred it up once or twice a day during that time to make sure all kernels were appropriately exposed to ambient air.
     

    NamibHunter

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    Thanks for doing the research MC10, superb write-up (commented in your blog as well). Your solid scientific approach is very impressive.

    Live on the Gulf Coast so relative humidity (RC) is often high: 55% to 65% is typical, but when the blue northen wind blows in early winter, RC can drop to the 30 % range, or below. Have figured out some time ago that storing powder in the garage is a bad idea. So now i have a thin sided wooden storage cabinet built to spec in my reloading room, and the combo of AC and a large dehumidifier machine keeps humidity reliably between 45% and 50%.

    BUT there is a complication: My testing has shown that when you take loaded ammo outside, there is a good chance that the case is not air tight, and will start to leak a little, because ambient pressure moves around from day to day creating a pressure differential that will move air in or out of your loaded cases, and that air carries humidity with it. That will gradually change the moisture content of the powder, no matter what the powder humidity was when you loaded the ammo in a controlled environment. This is especially a problem if you use light neck tension. I run 1.5 thou neck tension via a Whidden non-bushing FL sizer.

    So: Wanted to check if loaded rounds change weight due to humidity changes (water absorption) into the powder kernels inside the loaded round: Loaded 20 rounds in 6.5 CM, sealed 11 of them with the Ranger Sealant System (green liquid), left the other 11 unsealed as a control group. Weighed each case twice, via an FX120, around 15 minuted apart and wrote the consensus weight on the case with a sharpie. [Also checked if the evaporated solvent from the drying ink made a difference - it did not.]

    Then left them all outside in direct sunlight for 24 hours and then weighed them again. Two observations:

    1) Three of the 10 unsealed rounds increased their weight by 0.04 to 0.06 grains, the rest remained within measurement error of 0.02 gn.

    2) Only one of 10 sealed rounds changed weight. Probably the one i did not manage to seal properly.

    Repeated the experiment by leaving the ammo box in a sealed ziplock bag with a large capacity desiccant, also for 24 hours, and got largely the same results. One case changed weight by 0.14 grains after 48 hours (effect was small after 24 hours). That is significant and will increase ES.

    My preliminary conclusion was that even if you load humidity controlled powder (which is a very good approach), you still in have to worry about humid air leaking into or out of the loaded rounds, changing the burn rate and speed of the rounds in random ways, as not all cases will leak.

    Sealing the primers and bullets properly did help, but there is no guarantee that you got it right. It is easy to check for leaking cases by intentionally leaving your loaded ammo outside in the sun in high or low humidity weather for a day or two; and rechecking weight. Another good reason to get a milligram scale.

    And it might be better to figure out what is the average humidity where you are going to shoot that particular batch of ammo, and use the correct humidor to adjust the moisture content of your powder before you load, so if there is an air leak, it won’t matter too much. Of course, you will need to adjust the load as you vary humidity.

    I did shoot these rounds, and tried to measure speed, but my results were inconclusive, as the barrel was cleaned recently and i guess muzzle velocity has not yet stabilized. Plan to repeat the test soon, and would be very interested in the results you get if you try the same.
     
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    1moaoff

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    Every "batch, I don't load lass than 500 of anything usually.... of time I change jugs of powder I do a quick chrono check with 3 to 5 rounds just to make sure. I'm lucky though I walk 25 feet to test.
     

    mc10

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    Thanks for doing the research MC10, superb write-up (commented in your blog as well). Your solid scientific approach is very impressive.

    Live on the Gulf Coast so relative humidity (RC) is often high: 55% to 65% is typical, but when the blue northen wind blows in early winter, RC can drop to the 30 % range, or below. Have figured out some time ago that storing powder in the garage is a bad idea. So now i have a thin sided wooden storage cabinet built to spec in my reloading room, and the combo of AC and a large dehumidifier machine keeps humidity reliably between 45% and 50%.

    BUT there is a complication: My testing has shown that when you take loaded ammo outside, there is a good chance that the case is not air tight, and will start to leak a little, because ambient pressure moves around from day to day creating a pressure differential that will move air in or out of your loaded cases, and that air carries humidity with it. That will gradually change the moisture content of the powder, no matter what the powder humidity was when you loaded the ammo in a controlled environment. This is especially a problem if you use light neck tension. I run 1.5 thou neck tension via a Whidden non-bushing FL sizer.

    So: Wanted to check if loaded rounds change weight due to humidity changes (water absorption) into the powder kernels inside the loaded round: Loaded 20 rounds in 6.5 CM, sealed 11 of them with the Ranger Sealant System (green liquid), left the other 11 unsealed as a control group. Weighed each case twice, via an FX120, around 15 minuted apart and wrote the consensus weight on the case with a sharpie. [Also checked if the evaporated solvent from the drying ink made a difference - it did not.]

    Then left them all outside in direct sunlight for 24 hours and then weighed them again. Two observations:

    1) Three of the 10 unsealed rounds increased their weight by 0.04 to 0.06 grains, the rest remained within measurement error of 0.02 gn.

    2) Only one of 10 sealed rounds changed weight. Probably the one i did not manage to seal properly.

    Repeated the experiment by leaving the ammo box in a sealed ziplock bag with a large capacity desiccant, also for 24 hours, and got largely the same results. One case changed weight by 0.14 grains after 48 hours (effect was small after 24 hours). That is significant and will increase ES.

    My preliminary conclusion was that even if you load humidity controlled powder (which is a very good approach), you still in have to worry about humid air leaking into or out of the loaded rounds, changing the burn rate and speed of the rounds in random ways, as not all cases will leak.

    Sealing the primers and bullets properly did help, but there is no guarantee that you got it right. It is easy to check for leaking cases by intentionally leaving your loaded ammo outside in the sun in high or low humidity weather for a day or two; and rechecking weight. Another good reason to get a milligram scale.

    And it might be better to figure out what is the average humidity where you are going to shoot that particular batch of ammo, and use the correct humidor to adjust the moisture content of your powder before you load, so if there is an air leak, it won’t matter too much. Of course, you will need to adjust the load as you vary humidity.

    I did shoot these rounds, and tried to measure speed, but my results were inconclusive, as the barrel was cleaned recently and i guess muzzle velocity has not yet stabilized yet. Plan to repeat the test soon, and would be very interested in the results you get if you try the same.
    Thanks for sharing your testing! The results are convincing. I wasn’t expecting that much change within just 24-48 hours. That can throw off a load if you’re traveling to a different environment, especially if you chrono only once ahead of a multi-day match.

    Norma also published results from a loaded ammo humidity test in their article. They didn’t measure weight but did observe significant velocity swings over time.
    A7D9F9B5-C203-432E-88C2-1460B4A2E2E8.jpeg


    Humidity testing loaded ammo is definitely on my to-do list. I’d be interested in learning how neck tension plays a role, and re-confirming sealed vs non-sealed (like in your test). Then repeat over different time frames. This may be quite a few rounds…..
     

    NamibHunter

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    Thanks for sharing your testing! The results are convincing. I wasn’t expecting that much change within just 24-48 hours. That can throw off a load if you’re traveling to a different environment, especially if you chrono only once ahead of a multi-day match.

    Norma also published results from a loaded ammo humidity test in their article. They didn’t measure weight but did observe significant velocity swings over time.
    View attachment 7755810

    Humidity testing loaded ammo is definitely on my to-do list. I’d be interested in learning how neck tension plays a role, and re-confirming sealed vs non-sealed (like in your test). Then repeat over different time frames. This may be quite a few rounds…..

    Interesting! I know Vihtavuori also published a technical notice a few years ago stating that some of their powders chemically degrade over time and burn rate gets faster if stored for too long, which is less than ideal, as that can lead to over pressure situations. Probably true of many powders and most powder companies.

    I believe that same chemical degradation occurs in a loaded round as well. In addition to “cold welding” or whatever the correct technical term is.

    Have a buddy who hunts with a (correction: 338LM), he got an 8 lbs jug of N560 (if i recall correctly) so he did not need to adjust his load that frequently, and he ran into pressure problems after 3 or 4 years of indoor storage. Had to adjust his load.

    My point is that ammo stored for a long time can shoot at significantly faster speed for a variety of reasons:

    1) Humidity absorbed or lost over time into stored powder, or humidity absorbed into loaded rounds due to a leaky case (bullet/neck or primer not sealed). It will take drying out the powder inside the loaded round to speed up muzzle velocity. Flying through bright blue skies at much lower than sea level pressure will very likely cause some air exchange on the way up and again in the way down, and air at 40,000 feet can sometimes be bone dry, or super humid if you fly through cloud cover.

    2) Cold welding (galvanic corrosion) where the bullet and brass corrode and bond together tightly is a real thing. Just reseat 5 year old ammo and wait for the one or two that take immense force to budge.

    3) Chemical decomposition/degradation of powder inside the case (or the 8 lbs jug that you barely use) as the stabilizer chemical compound is consumed slowly over time. Not all powders do this equally fast, some are apparently way quicker to degrade than others.

    Would be interested to hear from folks who have had first hand experience with this problem (ammo speeding up and causing pressure problems).
     
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    parshal

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    I had an issue where one of my 65SS started showing pressure with the same 8 lbs. jug of R23. I talked to Alliant and the guy suggested that maybe the powder dried. It did make sense. I keep my powder in the crawl space under the house and bring up what I'm using. So, I'll have a few jugs of often used powder in the house. After that experience I now fill one pound containers from the eight pounders so less of it stays in the house.

    Since reading this thread on Wednesday I put a Kestrel Drop (I happened to have two) in the crawl space and one where I keep the smaller quantities in the house. They've remained constantly within 10% of each other between 26-36%.
     

    Emerson0311

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    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!

    That is great data. Appreciate all the trouble to do the testing and record and present in an accessible form.
     

    jtake

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    Keep in mind, relative humidity refers to the amount of saturation that particular temperature of air has. The dew point is the temperature at which the air is fully saturated (100% relative humidity). The actual amount of moisture in air having the same relative humidity can be drastically different depending upon the dew points. That is why dry climates with 100% humidity can still be dry, but 80% humidity in the during the summer in the east coast are pretty wet (and FLA is even worse), esp. when compared to the west coast.

    So unless your dew point remains constant throughout the year, working solely off of relative humidity will be very inaccurate with real world shooting. One really needs to combine the relative humidity with the dew point during the testing period in order to come up with how moisture in the air affects powder for repeatable results.
     

    parshal

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    Good info about the dew point. I’ll track that too throughout the year. I’d been meaning to do this for thankat few years anyway.

    I am mostly interested to see how consistent the environment is in the crawl space.
     

    NamibHunter

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    ‘Final (book) report’ on my 5 month humidity-seeps-into-loaded-ammo experiment: Some surprising results. Maybe a failed experiment has some benefit for others, so worth reporting. [Apologies for the length of the post.]

    History: Some 5 months ago, i loaded 40 rounds of 6.5 Creedmoor ammo (H4350, Lapua brass, 140 ELDM, weight sorted CCI450 primers), all via the FX120 - so weight is accurate to within 0.02 gn. [This is a repeat of an earlier experiment where 4 out of 40 rounds changed weight by up to 0.14 grains after loading the (unsealed) ammo and letting it sit outside for a week (humid summer conditions, US Gulf Coast).]

    Objective of the experiment: Wanted to see if sealant helped or not, and to see what neck tension works best to avoid air leaks into or from the cases that could potentially change water content of the powder, thus powder weight and powder burn rate, and therefore muzzle velocity and group size/vertical at long range.

    Loaded 40 cases, using mandrels/pin gauges mounted in the Porter Precision die, varying from 0.2615” (2.5 of nominal “neck tension”/interference fit if you ignore brass springback) to 0.2645” (very little actual grip, only springback of the brass provides about 0.2-0.4 thou of interference fit), in steps of 1.0 thou.

    Re-weighed all 40 rounds at periodic intervals, and finally shot them over a crony (Labradar) some 5 months later:

    Only two out of 40 loaded rounds changed weight by more than the measurement error (0.02 gn). Both rounds had extremely low neck tension (0.3 to 0.5 thou), both were unsealed cases, and both bullets could be rotated by hand. Could even pull the bullet out, and leave it like that to see how much weight change occurred over a 24 hour period due to humidity differences from day to day.

    Clearly, this is an impractically low amount of neck tension, and the loaded ammo is not robust enough for road travel over potholes, or air travel with large pressure changes in the luggage compartment of a plane.

    One round changed by 0.06 gn (maybe 6-7 fps effect) and the other by 0.08 gn (around 8-9 fps). [This change was about half of what i saw in the first experiment.] These two bad rounds would have taken an ES of 20 (good enough) to around 30 fps (not so great). SD would have moved maybe 0.5 fps (very little). In competition, this could cause two possible misses at 800 plus, depending on whether you are middle of node or edge of node.

    All 20 of the sealed rounds remained within 0.02 (measurement error) in weight, even the rounds where the rather impractical 0.2645 mandrel was used and only springback was holding the bullet in place, so no air leaks. It seems the sealant helps to glue the bullet in place and prevent air exchange. This is obviously a good thing.

    Then reseated all the bullets 30 thou deeper, to avoid bullet weld coloring the experiment, and measured seating force via the K&M force pack:

    Unsealed rounds expanded with the 0.2645 mandrel required 7-10 lbs of force to reseat, which is extremely low, while the 0.2640 expanded cases needed 20-28 lbs and several made a audible “thunk” (sudden change in COAL when the bullet weld broke loose). The variability in force needed to reseat the bullet was 2x higher than when the bullets were originally seated. The 0.2635 and 2630 expanded necks made a louder “thunk” sound (when the bullet is breaking loose, so probably more pronounced “bullet weld”). None of the unsealed rounds reseated smoothly or gradually, like they did when originally loaded.

    Sealed rounds: 0.2645 expanded necks needed 14-16 lbs to reseat, no thunk. The 0.2640 expanded necks needed 20-28 lbs, most smoothly glided in, but a few made an audible thunk sound (bullet weld). So bullet weld was less prevalent in the sealed ammo, but the problem was still there. Most reseated smoothly. The 0.2630 and 0.2635 expanded cases needed 35 to 48 lbs, which is 2-3x more variability than i am used to. The loud ones must have excessive bullet weld. So bullet weld is less prevalent in sealed cases, but not absent.

    Then shot all 8 batches/40 rounds: Each batch of 5 rounds had progressively less neck tension (by 1 thou). In total i fired 20 unsealed and 20 sealed rounds:

    Sealed rounds, low neck tension (0.2645 mandrel): These rounds were the most variable in terms of reseating force required (very disappointing!), and gave the highest ES (37 fps). So sealing cured the air leaks (same water content for the powder kernels), and it could reduce but not cure bullet weld, BUT it made the neck tension variability worse. So a net loss. Disappointing!

    Some of the unsealed bullets seated with very low neck tension could be rotated by hand, some not. [Sealed bullets could not be rotated, glued in place with the sealant.] Speed was about 10 fps slower for the two super low neck tension batches compared to the rest, but this difference is likely not statistically significant due to the tiny sample sizes of 10 vs 30.

    No significant difference in average speed between the other batches (2710-2716 fps).

    Possible conclusions from this rather messy (failed?) experiment:

    What we already know: Low neck tension is impractical. UNLESS you seal the neck - maybe. The glue/sealant helps to turn it into more robust ammo, and this also avoided humidity exchange with the ambient and prevented weight changes, and possibly maybe also avoided some potential speed changes. However, seating force variability went up. So still a bad idea to use very low neck tension, even if you seal the rounds.

    Also as a group of 20, the sealed ammo had the worst ES. That was surprising and rather disappointing. In future, i would not bother to seal target ammo, simply leave it in a sealed ziplock bag with the opened humidor pack inside. But i would load long and reseat all the bullets to the correct COAL before shooting them. [I would still seal hunting ammo that might be exposed to rain or get dunked in a stream when you slip and fall.]

    “Bullet weld” develops more frequently in unsealed cases, but both batches had this problem. Not enough benefit to justify the sealing effort. [Ammo was intentionally stored under adverse / extreme conditions for 5 months.]

    It is a good idea to control powder humidity in your reloading room via a large capacity electrical dehumidifier AND a suitable piezo electric humidifier to add humidity when needed. Yes more kit required.

    Sealing the rounds at the bullet / neck junction and at the primer helps with humidity changes of loaded ammo, but does not cure bullet weld, which has a more significant effect on speed. So load the bullets long and reseat the morning before the competition to the correct value. Pack an arbor press and a Wilson seater for reseating at the range. I got an SD of 11-13 fps for most of the batches, while my freshly loaded ammo usually gives 7-9 fps.

    Excessive neck tension has negative effects: The 0.2165 mandrel was too small and bullet seating force was very high: Effectively the soft lead core bullet was being used to resize the neck. Pull force was no different (using a Forster collet bullet puller die and a baggage scale) between rounds expanded via a 0.2615 and a 0.2625 mandrel. Even with the correct seating stem, a variable depth indent was left on the bullet nose - which is not good for BC variability.

    Tentative recommendations:

    I would guess that the cigar humidity control pack left inside the powder canister should help. Have “installed” these in two of my 8 lbs canisters, and will see if my ES comes down in future. Too early to tell.

    Before getting on a flight to go to a competition, i can see some benefit to weighing every case and writing the weight on the case body. Then weigh again after the flight. Trouble is you need a milligram scale and nobody in their right mind is going to fly a $650 force restoration lab scale in their luggage twice a month. The cheap small battery operated milligram scales using a standard load cell may or may not be accurate enough. But worth a try.

    Reseating the day of the competition will likely help to negate bullet weld if ammo was loaded a week or a month prior.

    Run adequate neck tension: 1.5 to 2.0 if cases are annealed. Can go to 2.5 to 3 thou if cases are not annealed, but watch out for damage inflicted by the seating stem.

    It is probably not worth sealing your target ammo. [But try it if you like - and let us know.]
     
    Last edited:

    Doom

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    South of the Mason Dixon Line.
    I did not comment on OP’s test when posted but did review it. It was referenced in another thread and I have posted some comments in the thread/post below. It’s long. Much of the comments relative to powder storage also apply to loaded ammunition.

     

    MCHOG

    Gunny Sergeant
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    ‘Final (book) report’ on my 5 month humidity-seeps-into-loaded-ammo experiment: Some surprising results. Maybe a failed experiment has some benefit for others, so worth reporting. [Apologies for the length of the post.]

    History: Some 5 months ago, i loaded 40 rounds of 6.5 Creedmoor ammo (H4350, Lapua brass, 140 ELDM, weight sorted CCI450 primers), all via the FX120 - so weight is accurate to within 0.02 gn. [This is a repeat of an earlier experiment where 4 out of 40 rounds changed weight by up to 0.14 grains after loading the (unsealed) ammo and letting it sit outside for a week (humid summer conditions, US Gulf Coast).]

    Objective of the experiment: Wanted to see if sealant helped or not, and to see what neck tension works best to avoid air leaks into or from the cases that could potentially change water content of the powder, thus powder weight and powder burn rate, and therefore muzzle velocity and group size/vertical at long range.

    Loaded 40 cases, using mandrels/pin gauges mounted in the Porter Precision die, varying from 0.2615” (2.5 of nominal “neck tension”/interference fit if you ignore brass springback) to 0.2645” (very little actual grip, only springback of the brass provides about 0.2-0.4 thou of interference fit), in steps of 1.0 thou.

    Re-weighed all 40 rounds at periodic intervals, and finally shot them over a crony (Labradar) some 5 months later:

    Only two out of 40 loaded rounds changed weight by more than the measurement error (0.02 gn). Both rounds had extremely low neck tension (0.3 to 0.5 thou), both were unsealed cases, and both bullets could be rotated by hand. Could even pull the bullet out, and leave it like that to see how much weight change occurred over a 24 hour period due to humidity differences from day to day.

    Clearly, this is an impractically low amount of neck tension, and the loaded ammo is not robust enough for road travel over potholes, or air travel with large pressure changes in the luggage compartment of a plane.

    One round changed by 0.06 gn (maybe 6-7 fps effect) and the other by 0.08 gn (around 8-9 fps). [This change was about half of what i saw in the first experiment.] These two bad rounds would have taken an ES of 20 (good enough) to around 30 fps (not so great). SD would have moved maybe 0.5 fps (very little). In competition, this could cause two possible misses at 800 plus, depending on whether you are middle of node or edge of node.

    All 20 of the sealed rounds remained within 0.02 (measurement error) in weight, even the rounds where the rather impractical 0.2645 mandrel was used and only springback was holding the bullet in place, so no air leaks. It seems the sealant helps to glue the bullet in place and prevent air exchange. This is obviously a good thing.

    Then reseated all the bullets 30 thou deeper, to avoid bullet weld coloring the experiment, and measured seating force via the K&M force pack:

    Unsealed rounds expanded with the 0.2645 mandrel required 7-10 lbs of force to reseat, which is extremely low, while the 0.2640 expanded cases needed 20-28 lbs and several made a audible “thunk” (sudden change in COAL when the bullet weld broke loose). The variability in force needed to reseat the bullet was 2x higher than when the bullets were originally seated. The 0.2635 and 2630 expanded necks made a louder “thunk” sound (when the bullet is breaking loose, so probably more pronounced “bullet weld”). None of the unsealed rounds reseated smoothly or gradually, like they did when originally loaded.

    Sealed rounds: 0.2645 expanded necks needed 14-16 lbs to reseat, no thunk. The 0.2640 expanded necks needed 20-28 lbs, most smoothly glided in, but a few made an audible thunk sound (bullet weld). So bullet weld was less prevalent in the sealed ammo, but the problem was still there. Most reseated smoothly. The 0.2630 and 0.2635 expanded cases needed 35 to 48 lbs, which is 2-3x more variability than i am used to. The loud ones must have excessive bullet weld. So bullet weld is less prevalent in sealed cases, but not absent.

    Then shot all 8 batches/40 rounds: Each batch of 5 rounds had progressively less neck tension (by 1 thou). In total i fired 20 unsealed and 20 sealed rounds:

    Sealed rounds, low neck tension (0.2645 mandrel): These rounds were the most variable in terms of reseating force required (very disappointing!), and gave the highest ES (37 fps). So sealing cured the air leaks (same water content for the powder kernels), and it could reduce but not cure bullet weld, BUT it made the neck tension variability worse. So a net loss. Disappointing!

    Some of the unsealed bullets seated with very low neck tension could be rotated by hand, some not. [Sealed bullets could not be rotated, glued in place with the sealant.] Speed was about 10 fps slower for the two super low neck tension batches compared to the rest, but this difference is likely not statistically significant due to the tiny sample sizes of 10 vs 30.

    No significant difference in average speed between the other batches (2710-2716 fps).

    Possible conclusions from this rather messy (failed?) experiment:

    What we already know: Low neck tension is impractical. UNLESS you seal the neck - maybe. The glue/sealant helps to turn it into more robust ammo, and this also avoided humidity exchange with the ambient and prevented weight changes, and possibly maybe also avoided some potential speed changes. However, seating force variability went up. So still a bad idea to use very low neck tension, even if you seal the rounds.

    Also as a group of 20, the sealed ammo had the worst ES. That was surprising and rather disappointing. In future, i would not bother to seal target ammo, simply leave it in a sealed ziplock bag with the opened humidor pack inside. But i would load long and reseat all the bullets to the correct COAL before shooting them. [I would still seal hunting ammo that might be exposed to rain or get dunked in a stream when you slip and fall.]

    “Bullet weld” develops more frequently in unsealed cases, but both batches had this problem. Not enough benefit to justify the sealing effort. [Ammo was intentionally stored under adverse / extreme conditions for 5 months.]

    It is a good idea to control powder humidity in your reloading room via a large capacity electrical dehumidifier AND a suitable piezo electric humidifier to add humidity when needed. Yes more kit required.

    Sealing the rounds at the bullet / neck junction and at the primer helps with humidity changes of loaded ammo, but does not cure bullet weld, which has a more significant effect on speed. So load the bullets long and reseat the morning before the competition to the correct value. Pack an arbor press and a Wilson seater for reseating at the range. I got an SD of 11-13 fps for most of the batches, while my freshly loaded ammo usually gives 7-9 fps.

    Excessive neck tension has negative effects: The 0.2165 mandrel was too small and bullet seating force was very high: Effectively the soft lead core bullet was being used to resize the neck. Pull force was no different (using a Forster collet bullet puller die and a baggage scale) between rounds expanded via a 0.2615 and a 0.2625 mandrel. Even with the correct seating stem, a variable depth indent was left on the bullet nose - which is not good for BC variability.

    Tentative recommendations:

    I would guess that the cigar humidty pack left inside the powder canister should help. Have “installed” these in two of my 8 lbs canisters, and will see if my ES comes down in future. Too early to tell.

    Before getting on a flight to go to a competition, i can see some benefit to weighing every case and writing the weight on the case body. Then weigh again after the flight. Trouble is you need a milligram scale and nobody in their right mind is going to fly a $650 force restoration lab scale in their luggage twice a month. The cheap small battery operated milligram scales using a standard load cell may or may not be accurate enough. But worth a try.

    Reseating the day of the competition will likely help if ammo was loaded a week or a month prior.

    Run adequate neck tension: 1.5 to 2.0 if cases are annealed. Can go to 2.5 to 3 thou if cases are not annealed, but watch out for damage inflicted by the seating stem.

    It is probably not worth sealing your target ammo. [But try it if you like and let us know.]
    Great work. Thanks for sharing.
     

    NamibHunter

    Desert hunter
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    Dec 26, 2018
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    Great work. Thanks for sharing.
    Thanks! Hope this is helpful to folks.

    For the folks who do not have time to read the ‘dissertation’ posted above:

    The initial hypothesis that some rounds can soak up moisture appears to be true due to a minority of leaky cases being present in each batch of hand loaded ammo (possibly due to deep scratches inside the neck - have a look with a bore scope, you already have several such cases). [These scratches are apparently caused post ignition by powder kernels being forced between case neck and bullet, as the case neck diameter start to enlarge, just before the bullet has time to get going.]

    Water content of the powder inside the case affects speed (a proven fact) and therefore will push up your ES some moderate amount: In my first experiment, the moisture soak seemed to add 14 fps to the ES - but that is true only if you are outside the node, it is far less if you are in the flat spot (node) on the speed graph. Wide nodes matter, but it hints that it is not the only effect: Variable neck tension and powder weight differences also drives ES. ‘Leaky’ cases contribute too via humidity changes. Higher neck tension helps to avoid moisture soaking into loader ammo, but it does not cure the problem. Hard to detect unless you drag a milligram scale to the match, which probably is not really practical…

    Sealing a case (with primer sealant) to make it water tight helps and hurts: Humidity soak goes away if you seal every case properly (not so easy in practice), but then neck tension becomes more variable: Sealant acts as a glue. You probably have to use very little and apply it exactly the same on each loaded round to see a net benefit, and not so easy to do by hand. I will not use it in future for target ammo, but will continue to use it for hunting ammo.

    ‘Bullet weld’ is real and is the dominant effect that dramatically changes bullet grip and therefore ES goed way up, so recommend you load long and reseat the morning of the match.

    It might help to transport loaded ammo in two double sealed ziplock bags with a humidor pack inside for humidity control (pick a relative humidity value similar to your reloading room conditions).

    Or simply ignore the problem and learn to live with your ES. Trying to control water content of loaded ammo is going yet another 10 feet deeper into the proverbial rabbit hole…. Where does it ever stop?
     
    Last edited:

    secondofangle2

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    Been obsessed with this lately too. Playing with 49% humidity packs. Most of my opened jugs (Utah. Humidity in garage usually about 20%) registered about 35% RH with a D2 drop. It takes a couple of days to equilibrate and get a good reading. I was taking out a sample into a mason jar and putting in a humidity pack for a day or two before reloading but it was getting tedious so I said F it and just dropped 2 humidity packs in each 5/8# jug. One pack seemed like it was taking too long to equilibrate to 49%. I haven’t shot this ammo yet but have long wondered what, besides powder temp sensitivity is giving me variable velocities between batches. Hopefully this works.

    I selected 49% packs because from what I’ve read, powder comes from factory at about 50% and 49% is what amazon had.

    I used to be pretty careless about leaving powder exposed to environment in many ways (eg leaving charged but unloaded cases laying out overnight or leaving powder in the dispenser). Not doing that any more!

    For they guys drying out powder or putting desiccant packs I’ve thought a lot about that and concluded that’s a no bueno idea. I worry that book and QL data may overestimate your safe load/pressures if their data are based on test pressures at 50% RH. (Indeed I’m surprised the QL program doesn’t have an input for RH%.). OTOH, if you have a load that’s safe with say 10% RH, there’s pretty much only one direction it can go namely slower/safer. I decided to go with the middle ground, ~ 50%

    Interested in others’ thoughts and observations.
     

    parshal

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    I keep most of my powder in the crawl space where I've put a Drop. The powder that I'm using is in my office where I also have a Drop. Humidity is well within 10% of each other and usually within 7%. I've not yet tested if there's a difference and whether I need to have the powder equalize in my office before use.
     
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    straightshooter1

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    Been obsessed with this lately too. Playing with 49% humidity packs. Most of my opened jugs (Utah. Humidity in garage usually about 20%) registered about 35% RH with a D2 drop. It takes a couple of days to equilibrate and get a good reading. I was taking out a sample into a mason jar and putting in a humidity pack for a day or two before reloading but it was getting tedious so I said F it and just dropped 2 humidity packs in each 5/8# jug. One pack seemed like it was taking too long to equilibrate to 49%. I haven’t shot this ammo yet but have long wondered what, besides powder temp sensitivity is giving me variable velocities between batches. Hopefully this works.

    I selected 49% packs because from what I’ve read, powder comes from factory at about 50% and 49% is what amazon had.

    I used to be pretty careless about leaving powder exposed to environment in many ways (eg leaving charged but unloaded cases laying out overnight or leaving powder in the dispenser). Not doing that any more!

    For they guys drying out powder or putting desiccant packs I’ve thought a lot about that and concluded that’s a no bueno idea. I worry that book and QL data may overestimate your safe load/pressures if their data are based on test pressures at 50% RH. (Indeed I’m surprised the QL program doesn’t have an input for RH%.). OTOH, if you have a load that’s safe with say 10% RH, there’s pretty much only one direction it can go namely slower/safer. I decided to go with the middle ground, ~ 50%

    Interested in others’ thoughts and observations.
    Likewise, I've been giving the issue of humidity a lot of attention lately, like since the first of the year. Here around Phoenix, AZ the RH tends to run between 10 and 20%. Sometimes below 10% and on a few occasions when monsoon rains happen, it can jump to 90% and stay up for a few days. That low RH around here acts like a dry sponge and really pulls moisture out of things fast (an issue hikers tend to underestimate).

    Using a Drop2, I found the RH for some of my powders that I've been using were between 35 and 40% and my never opened jugs and bottles were 45-50%. I'm still collecting data to see what kind of difference it makes, though I'm sure there is a difference, just hard to see when shooting in variable atmospheric temperatures. When charging cases, I've never left my powder out or exposed for very long, but now I'm making it a point to get the powder back in its container ASAP after charging and covering all the charged cases with the bullets before seating to further minimize exposure to the low RH.

    Recently, I've put a 49% humidity pack in a couple of those containers with powder that's at ~35% and will see soon see what kind of performance difference I'll get.

    This humidity issue for powder isn't anything of concern for those who live and reload in places that don't have such extreme RH. But, for those who live and reload in places where there's extreme low or high humidity, it can be a big issue. And it's surprising how few reloaders are even aware, though for a lot of them, it really doesn't matter for the type of shooting they do.
     

    Bryan Zolnikov

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    Good to see people monitoring the RH in the jug. So far, I haven’t seen any changes in baseline RH except for what may be measurement error (+\-.1%) in my jugs in atmospheric humidity ranges from 40-100% and temperatures ranging from 30-70 degrees F. One interesting thing I found was smaller powders have less RH relative to larger. My small N133 had ~56, N135 ~58, and RL26 ~60. I wonder if kernel size is a factor in powder humidity?
     

    OkieMike

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    bolt action reloading on youtube did a video 4 months back testing humidity vs velocity. looks like humidity has a huge impact in that video also.
    I think I watched that video too... If I remember correctly (and that's iffy nowadays) he surmised that once opened, and over time, the powder will "soak up" humidity/moisture which increases its weight... So each individual kernel of powder gets heavier than it was when it was sealed in the container... So as time goes by you end up dispensing less powder to arrive at your selected charge because the water adds weight.

    So even though the scale says the charge weighs the same, there's less powder.

    Or something like that.

    Mike
     
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    straightshooter1

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    I think I watched that video too... If I remember correctly (and that's iffy nowadays) he surmised that once opened, and over time, the powder will "soak up" humidity/moisture which increases its weight... So each individual kernel of powder gets heavier than it was when it was sealed in the container... So as time goes by you end up dispensing less powder to arrive at your selected charge because the water adds weight.

    So even though the scale says the charge weighs the same, there's less powder.

    Or something like that.

    Mike
    That's correct. And in addition to that effect of less powder per weight, the additional moisture in the powder slows down the burn rate. The inverse happens when powder dries out and often why we hear about reloaders using powder for quite a while and finding that it's faster than before (or slower in cases where they're in areas of high humidity).
     
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    reubenski

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    Powder in our region, Colorado, will drift to an eventual moisture content and then stabilize. It will happen slowly or quickly depending on how much you try to keep it sealed, but it will happen. Those of us who are wise to it, just expose the powder early on to get it over with so it is finally stable when we choose to load with it. And our conditions are more favorable. Less moisture= the powder produces higher velocity with less pressure. I want to move it to this state. And I don't want it constantly changing every time I open it to load from.