indoor powder storage, humidity, velocity

[Break Bad]

I recently noticed about a 60fps drop in velocity from 2820 to 2760 in my 6.5CM. I only have about 1500 rounds through the barrel, but consider I shot 4 or 5 matches with it, along with getting it hot during training. So I assumed it the lands were about done or I needed to start chasing. Regardless I had another match coming up so I screwed on a new barrel. Lo and behold using the rounds I loaded previously from the same 8 lbs jug of powder, i'm getting 2760. The load is 43gr H4350, 139scenars, 2.82 oal. I know different barrels behave differently, but I know 43gr is on the warm side and should be getting me over 2800.

Whats spooky to me is, I remembered this thread, in which the OP had the same issue with varget:
http://www.snipershide.com/forum/ubbthreads.php?ubb=showflat&Main=293955&Number=3335620

My powder is stored in doors, but this is Florida (humid) and sometimes I have the window open when I need to vent some fumes. Of course I do not leave the lid off my jug during all this, my lid is off only when I'm pouring powder in the dispenser. I am getting to the bottom of the jug, similar to the OP in the linked thread.

Without eliminating other causes, what further precautions can I take? (dehumidifier/storage options?)

I have an unopened jug (or three) and will use it to compare velocities and post results here.

Thanks for any feedback.

edit: Found a PDF with some good info on humidity, hydrometers, dehumidifiers, but no real data:
http://www.uniquetek.com/members/696296/uploaded/Humidity_and_Handloading.pdf

 

[Deadshot2]

Re: indoor powder storage, humidity, velocity

An old refrigerator is great to store a lot of powder and keep the humidity out of the equation. Set the temp so it's just below the average dew point and the air inside will be more than dry enough.

Don't know where exactly you live but for example, a quick check of the Pensacola area dew point shows it's 41 degrees now. Once you cool the air below the dew point then it starts loosing humidity.

Another approach is to just utilize a large ammo box, like one for 20mm or "Fuses", then use a large dessicant pack.

The neat part of using a refrigerator is that other essentials can be stored there too, like Beer.

 

[Break Bad]

Re: indoor powder storage, humidity, velocity

I knew I would regret getting rid of my garage fridge. But I have plenty of large ammo cans. Going to get some dessicant packs and a cheap hygrometer and go from there.

 

[BuzzBoss915]

Re: indoor powder storage, humidity, velocity

Go ahead, if you think that will protect your powder from changing, but there are incidents where powder left undisturbed "can" deteriorate over a period of several years. Personally, I just keep the lid screwed on and have never had a problem in 40 years of storing powder...but that don't mean it can't happen.

Your best defense is looking for a gray and rusty color as you pour it into a powder measure. Never happened to me but I've seen photos and it happened to a friend recently. (IMR 1# metal can)

So rare that I refuse to get excited about it. Lots of WWII surpuls powder was stored in paper bags and cardboard "cans" and I have used a lot of it and never saw a problem. BB

 

[Fred_C_Dobbs]

Re: indoor powder storage, humidity, velocity

Smokeless powder is extremely hygroscopic and can absorb a huge amount of moisture before the granules will swell. So over time, it's entirely possible for a given volume of powder to gain weight. And if you're measuring moisture-heavy powder by weight, your load will contain less powder and more water than before it go so damp, so you're obviously going to get fewer FPS.

A few years back I chrono'ed a batch of fresh-loaded bullets using an old, established formula and powder from a 1# bottle that had been opened about 10 months. It had lost quite a few FPS so I asked around to my reloading buddies what might have caused the drop. One of them seemed certain it was a humidity problem so I put a packet of silica gel desiccant in the bottle and left it a couple of days. My MV jumped, so I left it another day and repeated. It jumped again.

In all, it took five days before the MV stopped climbing. At the start I was getting on average 3030 fps from a 43.7-gr charge. Dried out, I was getting 2995 fps from 41.4 grains. More than 5% less charge by weight and it only lost 35 FPS. If I hadn't been checking it incrementally, and if I'd loaded 43.7 grains of dried powder, I'd probably have blown that rifle to helen gone.

That sounds impossible, and Alliant customer service told me it was (in very diplomatic terms), but when I got to the bottom of that bottle of (artificially dried) powder, I tested it against a fresh bottle. The new bottle was from the same lot, bought at the same time and stored side-by-side the old bottle. The 3-round average MV of 40.0-gr charges were within 5 FPS of each other, and were within 30 fps of the published figure for a 40.5-gr charge.

I have to believe that old bottle of powder just absorbed that much moisture. So now when I open a new bottle, I put in a packet of desiccant first thing and leave it for a week before I run the first loads from it. Then I test light charge weights, just to confirm I know what's happening to my MVs without running risky pressures. And it's a big enough packet of silica gel that I know I'm going to have near-zero moisture all the way to the bottom of that bottle, which should mean my powder's 'power' isn't going to weaken.

When I switch bottles of powder, the silica gel goes in the microwave for a bit to "recharge" it, then it goes back into service in the new bottle.

 

[Break Bad]

Re: indoor powder storage, humidity, velocity

I'm not as concerned with long term storage as I am with exposing powder by frequently opening a jug. Even in A/C here in FL it can get very sticky. Summertime with a/c set at 75 it should be about 50% humidity. With an older a/c unit, bad coils, and a vent blowing on the reloading bench....stuff like that. Hopefully Yes, I'm getting excited over nothing.

 

[Break Bad]

Re: indoor powder storage, humidity, velocity

Great info thank you Mr. Dobbs. I'll give it a go.

 

[BuzzBoss915]

Re: indoor powder storage, humidity, velocity

Yes, interesting Fred. But, I have to wonder, if it is any kind of a problem, why the manufacturers don't include desiccant just like in a lot of prescription drugs? They have to know that bottles are opened and closed all the time and left on a shelf until next year. And, they know that some people live where there is humidity. Why somebody chooses to live in Seattle is beyond me, but whatever? Maybe they should, but what it says to me is; it's not a problem or they would be addressing it. BB