Home Forums Reloading Big Game Rifles Smokeless powder - does it “dry out”?

Had an interesting experience yesterday. I have had 20 rounds of .257 Weatherby all prepped, primers and powder charged with 75.5 grains of H1000, weighed out of a calibrates Hornady Auto charge. They have been sitting in my cabinet, undisturbed for (hate to admit it) about 6 months.

Yesterday I decided to finish the project and seat the bullets. As I started to get things ready I thought it would be good to check the powder charges just to make sure they truly hadn’t been disturbed. Case after case was emptied onto the freshly calibrated scale and weight was 2 or 3 10ths light. It wasn’t a lot, but consistently lighter...with weights of 75.2 or 75.3 being the majority...none at 75.5.

I mixed all of that powder back into the 5 or so pounds I had left in the jug and then recharged all of the cases at the 75.5 and capped them with the bullets.

So, if powder is left exposed to the air, does it “dry out”? If so, what effect, if any does it have?

It only ends up being a 4/10’s of a percent difference in charge by weight, but has me wondering.

Thanks,

300winnie

I believe that it might have something to do with how dry your area is.

Around here it is about 10 or less.

Sometimes like the last few days it has gone up to 98 +-.

It may off gas a bit.
Hence the smell when you open a can.
Pretty sure it is piped around ammunition plants as a slurry before being formed.

It's got to "dry out " a bit. It's got volatile chemicals in a cellulose matrix. Some of those have to bleed off or oxidize over time. I have no idea how much, or at how fast a rate, or if that's what happened with this particular situation though.

Moisture clings to certain types of powder. If left exposed to open air, the weight of a fixed amount can/will vary along with the humidity level of the area.

I wouldn't say clings, that reminds me of dew on foliage.

I don't leave powder out even for more than a minute or two. As soon as I get the powder measure set for the charge a cap goes on. If I am loading a bunch of cartridges, I'll only load a limited amount with powder and then I'll seat the bullet. I may have loaded up to a 100ea 223 cases before seating bullets. But I was loading a bunch for PD shooting.

If I forgot and left cases with powder in it that long, I'd poor the powder out.

I couldn't compare to dew on foliage, as foliage consumes some of the dew. Powder doesn't. But I guess if it is present, moisture lies on the surface in one form or another. The event is explained in one of my reloading manuals. I could verify, but I'm not going though the 27 I have, to find it. Sorry.

Shooters World says smokeless powder has an affinity to moisture, attracts it. Not likely a magnetic personality in the purest form, but relative.

I would say absorbs moisture.

From an article elsewhere:

He's Sven Eric Johansson, head of ballistics at Nexplo/Bofors at the time.

That's what I understood as well, that single-base powders are more hygroscopic. I read it in some arcane source from the 1940's.

According to Hodgdon, H1000 is a double-base powder which contains diphenylamine as a stabilizer.

I would say some types of powder aDsobs moisture.

But the main thing, we agree that powder volume can/will weigh differently due to the presence &/or amount of moisture.

I don't know know if it dries out or absorbs moisture, but I've used several IMR powders in recent years that were manufactured in the late '60s or early '70s and they worked fine.