Humidity affect powder volume?

[BigMahi]

Two weeks ago I opened a new jar of Varget, one dip with the Lee 3.1cc powder dip measured about 42.3 grains. I left the jar open by accident in my basement which is humid. Then tonight, with the SAME dipping and leveling off method as before and same dipper, one dip yielded around 43.8 grains. Aside from being an idiot for leaving the jar open, does powder absorb moisture? If so, how does that affect the round? Is there anything I should or could do to compensate for the added moisture? Or is the remaining powder fertilizer?

Thanks.

PS. I calibrate my scales each time so assume that's not a factor.

 

[CK_32]

Re: Humidity affect powder volume?

If its damp and not a dry enviorment I'd say scrpa that jar and go get some a new one. Dont even bother chancing it. I've never had it happen or knew anyone who's had this happen but I know its not safe.

From what I think you would either end up with a bunch of dud rounds which are never good or the other thing I think would come of it would be blow the case from having extra pressure and have the water heat up on a hot day and blow your breach or damage the gun and you in some way. I just dont think it is worth chance and would highly recommend scrapping that tub and just be on the safe side and be sure not to do that again.

 

[EddieNFL]

Re: Humidity affect powder volume?

Zediker (IIRC) wrote about this. Powder is very hygroscopic. Let it stabilize in a controlled climate and I'll bet you won't notice any difference at the range.

 

[BigMahi]

Re: Humidity affect powder volume?

So once I get my dehumidifier up running, I should leave the jar open and check if it has returned to it's usual volume (42.3 grains per 3.1cc's)?

Ck_32 - Thanks for the warning, my first thought was to chuck it but it wasn't damp, just humid and I noticed the slight increase in weight of the powder given the same volume and wanted to see if i can rehab it.

 

[Grump]

Re: Humidity affect powder volume?

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: BigMahi</div><div class="ubbcode-body">So once I get my dehumidifier up running, I should leave the jar open and check if it has returned to it's usual volume (42.3 grains per 3.1cc's)?

Ck_32 - Thanks for the warning, my first thought was to chuck it but it wasn't damp, just humid and I noticed the slight increase in weight of the powder given the same volume and wanted to see if i can rehab it. </div></div>

Either stir the jug twice a day or put it in a more open-top container with the powder about only 2 inches deep.

THEN you get to think about loss of the more volatile components, like ether and acetone and alcohol residues...

Better, I think, to just leave it open, in the jug, in 10% or less humidity for the same amount of time.

THEN blend it with two or more pounds of unopened stuff. If a plastic container, anti-static it first and stir thoroughly.

IF any of these variables could result in a blown-up rifle, your loads are way too hot anyway. We don't want to use up all of our safety margin, but there IS a generous safety margin.

Best evidence of safe or not is, IMO, velocities. To "good" is a way BAD thing. Just load to velocity like the factories do (safe published or proven load, SAME rifle) and you'll be okay.

 

[XTR]

Re: Humidity affect powder volume?

I'm sure that somewhere about 20 yrs ago I had this discussion about reloading. The point someone was making was that because powders are hygroscopic its better to load by volume than weight.

What you've gained is 1.5gr of water in your powder charge, how will it effect velocity/pressure? I don't know, powder may burn a bit slower, but the water displaces volume, but you are not adding more propellant.

Personally, I'd load it, chrono it and see where it hits. I'm betting you can't tell the difference.

 

[Fred_C_Dobbs]

Re: Humidity affect powder volume?

Three weeks ago I finished a bottle of Varget and opened a new one. Both bottles were the same lot number, bought at the same time and kept on the same shelf. MV jumped 30 fps with the new bottle. I asked around and came to the conclusion that the old powder must have absorbed a little moisture, making a given volume of powder a tad heavier.

About that time, I started in on a year-old bottle of RL-19 that hadn't been opened in six months. I got froggy and decided I wanted rid of all that moisture so I put a packet of silica gel desiccant inside the bottle. I didn't care how much moisture it held, I just wanted a given charge to produce a predictable velocity, month in, month out. The only way I could figure to get there was with a BIG packet of desiccant that would guarantee 0% humidity.

I shot test loads for the next two consecutive days and the MV kept increasing (by 60 fps one day and another 80 fps the next). So I left it undisturbed for three days and tried it again. In those three days, MV jumped almost another 500 fps. It had stabilized after five days but the weight of a charge necessary to drive a 100-gr Nosler Partition bullet to 3000 fps had dropped by five full grains, more than 9% (nine percent).

I store my powder in a closet inside the house, which has central heat and air and stays at 70°F year round. The roof does not leak and there is no plumbing or any electronic equipment anywhere near this closet. I also keep a box of calcium chloride desiccant in the closet.

I wrote Alliant and told them what had happened. They blew me off. I might not be the sharpest Crayola in the box but there's no way in hell I could miss a difference of 9% by weight.

So now the plan is to open every new bottle an add a packet of desiccant, give it a week and then test for MV. And that's right where it should be 10 years from now.

Did I mention this desiccant is sized for two cubic feet of space?

 

[XTR]

Re: Humidity affect powder volume?

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: Fred_C_Dobbs</div><div class="ubbcode-body">Three weeks ago I finished a bottle of Varget and opened a new one. Both bottles were the same lot number, bought at the same time and kept on the same shelf. MV jumped 30 fps with the new bottle. I asked around and came to the conclusion that the old powder must have absorbed a little moisture, making a given volume of powder a tad heavier.

About that time, I started in on a year-old bottle of RL-19 that hadn't been opened in six months. I got froggy and decided I wanted rid of all that moisture so I put a packet of silica gel desiccant inside the bottle. I didn't care how much moisture it held, I just wanted a given charge to produce a predictable velocity, month in, month out. The only way I could figure to get there was with a BIG packet of desiccant that would guarantee 0% humidity.

I shot test loads for the next two consecutive days and the MV kept increasing (by 60 fps one day and another 80 fps the next). So I left it undisturbed for three days and tried it again. In those three days, MV jumped almost another 500 fps. It had stabilized after five days but the weight of a charge necessary to drive a 100-gr Nosler Partition bullet to 3000 fps had dropped by five full grains, more than 9% (nine percent).

I store my powder in a closet inside the house, which has central heat and air and stays at 70°F year round. The roof does not leak and there is no plumbing or any electronic equipment anywhere near this closet. I also keep a box of calcium chloride desiccant in the closet.

I wrote Alliant and told them what had happened. They blew me off. I might not be the sharpest Crayola in the box but there's no way in hell I could miss a difference of 9% by weight.

So now the plan is to open every new bottle an add a packet of desiccant, give it a week and then test for MV. And that's right where it should be 10 years from now.

Did I mention this desiccant is sized for two cubic feet of space? </div></div>

This is the point that someone was trying to make to me back then. I gotta wonder if you loaded by volume and not by weight, how much difference would it make?

Another lesson here is to load in batches. If you load in a larger batch I would assume that your MV across the batch would be consistent.

 

[Fred_C_Dobbs]

Re: Humidity affect powder volume?

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: XTR</div><div class="ubbcode-body">This is the point that someone was trying to make to me back then. I gotta wonder if you loaded by volume and not by weight, how much difference would it make?...</div></div>
Loading by volume should cure the problem but I see two new problems with that approach. How accurately can you measure volume ...to the tenth of a grain?? How do you make a scoop that's accurate to four or five <span style="font-style: italic">granules</span> of powder? And how often do you adjust charge weight (meaning how many of these hyper-accurate scoops will you have to make?).

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: XTR</div><div class="ubbcode-body">...Another lesson here is to load in batches. If you load in a larger batch I would assume that your MV across the batch would be consistent. </div></div>
True that.

One concern the guy at Alliant had was that my desiccant could dry out the powder unevenly. I forget if it was while learning to scuba dive or learning to fly but somewhere I learned that water vapor has 40-50x the pressure of dry air. There's no way in hell that the powder on top is packed so tightly as to prevent the powder granules in the bottom of the bottle from off-gassing their moisture once the air on top dries out. Even if I'm wrong, the damp powder on the bottom is less dangerous that the dry stuff on top, which is what I've already tested.

The only real problem I see with using the desiccant is that even factory-fresh powder will have just a smidge of moisture in it so completely dry powder should have more power per grain than the factory stuff. Read: potential <span style="font-style: italic"><span style="font-weight: bold">kaBOOM!</span></span> Which puts the oneness on the shooter more than ever to start low and approach dangerous pressures incrementally.

 

[XTR]

Re: Humidity affect powder volume?

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: Fred_C_Dobbs</div><div class="ubbcode-body">
One concern the guy at Alliant had was that my desiccant could dry out the powder unevenly. I forget if it was while learning to scuba dive or learning to fly but somewhere I learned that water vapor has 40-50x the pressure of dry air. There's no way in hell that the powder on top is packed so tightly as to prevent the powder granules in the bottom of the bottle from off-gassing their moisture once the air on top dries out. Even if I'm wrong, the damp powder on the bottom is less dangerous that the dry stuff on top, which is what I've already tested.

The only real problem I see with using the desiccant is that even factory-fresh powder will have just a smidge of moisture in it so completely dry powder should have more power per grain than the factory stuff. Read: potential <span style="font-style: italic"><span style="font-weight: bold">kaBOOM!</span></span> Which puts the oneness on the shooter more than ever to start low and approach dangerous pressures incrementally. </div></div>

I do waste management and you'd be surprised how much moisture content can differ over a vertical column of any material. Classic waste acceptance violation is that a container has had sorbants added to the top, the moisture there is sorbed so it appears dry, but there is still free standing liquid in the bottom.

As long as you mix the material after you remove the desiccant you'll be ok.

 

[Fred_C_Dobbs]

Re: Humidity affect powder volume?

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: XTR</div><div class="ubbcode-body">I do waste management and you'd be surprised how much moisture content can differ over a vertical column of any material. Classic waste acceptance violation is that a container has had sorbants added to the top, the moisture there is sorbed so it appears dry, but there is still free standing liquid in the bottom....</div></div>
I'm gonna assume you're not talking about a container full of highly absorbent material. When I started, my 45-grain charge of RL-19 contained five grains of water. That makes 40 grains of powder and five grains of water. And it wasn't used to sop up a spill, it sucked up five grains of humidity out of the air. I'd say that qualifies as highly absorbent. I'd venture to guess the attraction is <span style="text-decoration: underline">so</span> <span style="text-decoration: underline">strong</span> it is impossible for the concentration to be lopsided inside the bottle (provided it's been sitting a while) even without there being any desiccant in it.

The bottle of Varget I just finished off -- which was stored on the same shelf -- had been open even longer but obviously had absorbed relatively little water. I'm left to conclude that either RL-19 absorbs an unusually high amount of water or that there was some sort of voodoo acting on that one bottle that I have yet to finger out.

 

[BigMahi]

Re: Humidity affect powder volume?

Thanks a lot for the helpful replies. Turns out humidity is also a factor for internal ballistics. That said, I will now leave the jug of powder in out for a few days with the dehumidifier running and load up a few rounds well within the safe ranges and see how they shoot.

Also, lesson learned, I usually load no more than 3/4 pound in one session so I will divide the 8 pound jug into 1 pound containers. I realized removing the paper backing from under the lid reduces the air seal so I am adding a layer of plastic saran wrap under the lid. Hopefully this reduces the variance across loads.

Robert Rinker, in his book Understanding Firearms Ballistics mentioned how they old theory was the drier the powder the better but then they discovered that allowing a bit of moisture improved the powder. But then again everything in moderation.

 

[Fred_C_Dobbs]

Re: Humidity affect powder volume?

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: BigMahi</div><div class="ubbcode-body">...Robert Rinker, in his book Understanding Firearms Ballistics mentioned how they old theory was the drier the powder the better but then they discovered that allowing a bit of moisture improved the powder....</div></div>
But if you go that route, the problem is how to maintain moisture levels at "a bit." IMHO, that's an impossible task for Joe Sixpack, which is why I went with the 0% solution.

BTW, yesterday I bought a new bottle of RL-19. Today I tested it -- undoctored -- against my old uber-dry bottle. Same bullet, same charge weight, alternating firing one round from each bottle, 90 seconds between shots, three rounds of each, the old, dry powder was faster by 5 fps.