Effect of humidity on nitrosellulose

[THOMAST]

Hi gents,
Seeing as cotton is a component of propellant, I was wondering if anyone has an idea (quantitatively) of the real effect different humidity levels will have on exposed propellant? Lets use an extruded propellant as an example.
We have all heard of propellant drying out (loosing moisture) in low humidity conditions leading to higher volume to weight ratio when weighing propellant, leading to higher velocities and pressures, and vice versa.
We're all told to keep the propellant in its original container, sealed properly when not in use.
Once ammo has been loaded the propellant is sealed in the cartridge and humidity changes wont have an effect on the propellant in the cartridge anymore
When visiting a local propellant manufacturing plant I was told that the batches of propellant is tested at a specific temperature (21ºC) and humidity level (60%) as a standard.
So I was wondering if you kept a volume of propellant in a container, exposing the propellant to different levels of humidity and weighing the sample each time on a decent scale what weight differences would be present?
Exposure time would also be important, my thinking being that the longer the propellant is exposed to a certain level of humidity, the bigger the effect would be.
The question is How Much difference?
Any ideas/thoughts?

 

[BoydAllen]

There was a very good article in Precision Shooting Magazine (no longer in business) in which this very subject was explored with VV 133. Powder was measured into open cartridge cases, by weight, and then it was dried, humidified and using the same powder in the same cases, bullets were seated, and velocity data collected. The gain in weight from bone dry to fully humidified was 2%, the out of the jug weight was somewhere in between, and the spread of velocities from the extremes of moisture was, I believe, 320 FPS, the dry powder yielding the higher velocities. Correct me if my memory does not serve. You can do your own experiment. Friends did a less rigorous test of a different powder and found a 250 FPS difference between somewhat drier than from the container, and more humidified. I think that these sorts of results would be the same with any powder.

 

[THOMAST]

Thank you BoydAllen, those are interesting numbers. Do you know if temperature at time of shooting was taken into consideration as well?

 

[LongRanger]

I ran a test a few months ago to check the effect of powder left open overnight and found the weight had increased enough the next day to possibly affect rifle tune. As I recall, the change was .2 grains more for a 60 grain charge.

Frank B.

 

[THOMAST]

Thanks LongRanger.
Reading through some academic articles on a similar subject I made the conclusion that the increased moisture content due to high humidity levels has an effect on the burn temperature of the propellant (cooling the propellant down in effect) which would lead to lower pressures/velocities. Couple that with the reduced volume of propellant being charged (after weighing "wetter" propellant) and these two factors could go some way in explaining the drop in velocity as indicated by BoydAllen
Now throw in ambient temperature into the works...
Aint reloading great? )

 

[BoydAllen]

Another story that has some relation to this problem came from a famous gunsmith and competitor, who preloaded for a major match over a period of time, in batches, when the weather varied quite a bit as to humidity. Each time that he loaded one of the batches of ammunition for his 6PPC he tested to see how much powder was required to reach his desired velocity, and loaded that weight. There were probably something like five or six separate sessions, over several weeks. The interesting part is that the extremes of these weights were a grain and a half apart. The powder was 133. Later, before the match, when a shooting buddy expressed the opinion that this procedure was a mistake, the fellow who had loaded the ammunition pulled loads from all of the batches, and shot groups with the mixture of charge weights. The groups were good, not the disaster that had been predicted by his friend. Looking back, it would have been interesting if those groups had been shot over a chronograph.

 

[amlevin]

A good use for an old refrigerator. Just like welders will store flux coated welding rod in these to protect from high temp/humidity, why not with powder?

I'm fortunate that I live in an area where humidity averages around 60% and the temp in my reloading area, 68 degrees average. No real large swings in either.

Maybe one of those Temp/Humidity controlled Cigar Humidors would be the ticket? Only "Two Grand" on Amazon http://www.amazon.com/Prestige-Import-Group-Temperature-Controlled/dp/B008EODL14