answer me this

Quote from Accurate Arms Reloading Manual

"Still another effect of storing powder at high temperature is to drive out some of the moisture, as well as some of the volatile solvents such as ether and/or alcohol and/or acetone, that normally remain in newly manufactured powder.

Once driven out, the volatile solvents cannot be recovered, but the moisture content of the powder will increase or decrease upon exposure to the air, more or less, depending on the relative humidity. This property of giving up moisture or taking on moisture from the air is called hygroscopicity.

When exposed to the atmosphere, powder will lose moisture or gain moisture, depending on the relative humidity."

I think what is important to us as reloaders is the following quote from Accurate Arms:

"Another effect of powder temperature on the ballistic performance of ammunition becomes of some importance at the time of loading. That is the effect of temperature on the gravimetric density (sometimes called bulk density) of the powder. The gravimetric density of powder is the ratio of the weight of powder which fills a particular volume (under carefully prescribed conditions of filling), to the weight of water that would fill the same volume. The gravimetric density of a powder is important because it determines the amount of powder that will be dispensed from a volumetric measure of a particular capacity."

"Gravimetric density depends on several characteristics of the powder, but it has been found in general that increasing temperature of the powder causes a reduction in the gravimetric density. The increase in gravimetric density amounts to about one percent for a temperature change of 20 degrees F"

About handloaded ammunition:

"Ammunition is not hermetically sealed. Such ammunition "breathes" during temperature changes, because the air inside expands at high temperature and leaks out into the atmosphere, and it contracts at low temperature, drawing in air from the surrounding atmosphere. The powder inside the cartridge is thus exposed constantly to fluctuations in humidity of the surrounding atmosphere."

You want to get really confused, read more about humidity. Is the air more or less dense when the Radio Shack gizmo is reading 90%? Is the air more or less dense when the Radio Shack gizmo is reading 30%?

GW
 
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I mentioned adsorption a while back but it wasnt a flaming post so you must have missed it. Howcome you cant take the word of people who use their real names and actually shoot "goodgroups". Anybody who actually shoots or places in the top knows something happens when humidity, temp and all that changes. The non believers usually pre load since it dont matter in their eyes.
 
Gary Walters said:
"Still another effect of storing powder at high temperature is to drive out some of the moisture, as well as some of the volatile solvents such as ether and/or alcohol and/or acetone, that normally remain in newly manufactured powder.

Once driven out, the volatile solvents cannot be recovered, but the moisture content of the powder will increase or decrease upon exposure to the air, more or less, depending on the relative humidity. This property of giving up moisture or taking on moisture from the air is called hygroscopicity.

When exposed to the atmosphere, powder will lose moisture or gain moisture, depending on the relative humidity."

I think what is important to us as reloaders is the following quote from Accurate Arms:

"Another effect of powder temperature on the ballistic performance of ammunition becomes of some importance at the time of loading. That is the effect of temperature on the gravimetric density (sometimes called bulk density) of the powder. The gravimetric density of powder is the ratio of the weight of powder which fills a particular volume (under carefully prescribed conditions of filling), to the weight of water that would fill the same volume. The gravimetric density of a powder is important because it determines the amount of powder that will be dispensed from a volumetric measure of a particular capacity."

"Gravimetric density depends on several characteristics of the powder, but it has been found in general that increasing temperature of the powder causes a reduction in the gravimetric density. The increase in gravimetric density amounts to about one percent for a temperature change of 20 degrees F"

About handloaded ammunition:

"Ammunition is not hermetically sealed. Such ammunition "breathes" during temperature changes, because the air inside expands at high temperature and leaks out into the atmosphere, and it contracts at low temperature, drawing in air from the surrounding atmosphere. The powder inside the cartridge is thus exposed constantly to fluctuations in humidity of the surrounding atmosphere."

You want to get really confused, read more about humidity. Is the air more or less dense when the Radio Shack gizmo is reading 90%? Is the air more or less dense when the Radio Shack gizmo is reading 30%?

GW
Click to expand...

Wow. Thank you Gary for your post. Very interesting. I think I now see why there's so much confusion about this. There is contradictory information. One source says that powder is not hygroscopic and another says it is. If I get time today, I'll link a few contradictory bits here and see what we can make of it. Thanks again. I knew somebody would get some data here eventually if I pressed it enough. Only took 5 pages and a week and a half!:)
 
Dusty Stevens said:
I mentioned adsorption a while back but it wasnt a flaming post so you must have missed it. Howcome you cant take the word of people who use their real names and actually shoot "goodgroups". Anybody who actually shoots or places in the top knows something happens when humidity, temp and all that changes. The non believers usually pre load since it dont matter in their eyes.
Click to expand...

Don't look now but it looks like someone's prejudices are showing!:eek:


Sorry Dusty. I did miss your post. Just like you must have missed mine when I said that I didn't care what Tony said, I cared WHY Tony said it. In other words, I wasn't asking what color the sky is, I was asking WHy is it that color?
And it seems you missed my post about my competing and you missed my post about how I just pay attention to temperature because I don't even own a humidity gauge. So I'd say we're even. I missed one of your posts and you missed three of mine. But I understand you were upset because I don't use my real name here. You are just going to have to get over that part though or it will trip you every time. Sorry.
 
Just for fun, I weigh out 29 grains of 820-04. While it was in the scale pan,
I added 2 grains of water via a straw. Didn't plan on 2 grains, just got lucky. The scale now sitting at 31. The powder was stired untill it was
all sticking together, as though magnetic. An hour and a half later, It weighed
29 grains.That it was absorbed or ADsorbed, I don't know, but it gave it back
to the air in that time. My pocket wonder said 45% @ 72 deg F. No doub't
it would have returned much slower in high humidity. I'm certain, that had
I been weighing at the range, I would have gotten less powder.
 
Bob Kingsbury said:
Just for fun, I weigh out 29 grains of 820-04. While it was in the scale pan,
I added 2 grains of water via a straw. Didn't plan on 2 grains, just got lucky. The scale now sitting at 31. The powder was stired untill it was
all sticking together, as though magnetic. An hour and a half later, It weighed
29 grains.That it was absorbed or ADsorbed, I don't know, but it gave it back
to the air in that time. My pocket wonder said 45% @ 72 deg F. No doub't
it would have returned much slower in high humidity. I'm certain, that had
I been weighing at the range, I would have gotten less powder.
Click to expand...

Thank you Bob. That is very interesting too. I think that shows powder is not hygroscopic (or at least the powder you were using) but it may lend itself to adsorption. I sure wish we could find some lit on adsorption rates of powder, humidity levels required to be adsorpic, reactions to static electricity if there are some, or how does containment of powder in a pill bottle affect adsorption.

In my humble tests, there was one morning where the humidity was so high that all the paper I was using to write down information turned into a leather like substance and got all wrinkly (now that's certainly hygroscopic!). I filled up my Harrells and threw 52 clicks of n133 and shot it over the chrono. The temp was 55 degrees and the load went 3265. That same evening, the temp went back down to 55 degrees after being near 90 mid-day and the humidity was back to normal levels of around 30 to 40 percent and the paper felt normal. I loaded up 52 clicks again from the powder thrower and the bullets were going 3258. So I could not tell that the high humidity had affected anything. It seemed to be pretty consistent according to temp alone? I don't know. I'm just throwing this out there.
 
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The Lapua Shooting and reloading manual 2nd edition does say that
burning rate is affected by a number of things as we all know, moisture
content being the last item listed. That is on page 34.
I have seen other information, and a graph, but can't locate it.
 
http://www.statemaster.com/encyclopedia/Hygroscopic


"Both black powder and black powder substitutes are very hygroscopic - that is - they have a high tendency to absorb moisture from the air. When these powders absorb moisture, the powder burns slower. Smokeless powder is not hygroscopic in nature, a nice benefit of nitrated cellulose."



"Smokeless powder allowed the development of modern semi- and fully automatic firearms. Burned blackpowder leaves a thick, heavy fouling which is both hygroscopic and corrosive . Smokeless powder fouling exhibits none of these properties. This makes an autoloading firearm with many moving parts feasible (which would jam or seize under heavy blackpowder fouling). "


http://www.saami.org/glossary/display.cfm?letter=P



I'm still looking for lit on adsorption qualities of smokeless powder. It's a bit tougher.
 
For what it is

There are 2 things I have observed in 25+ years of benchrest that may hint at the humidty issue.

When it is high the first passes of the brush will feel like the fouling is softer.

8208 powders are generally easier to keep in tune in dry climates while 133 is better in wet climates.

This sounds like the RH is a factor that affects the powder fouling rather than the actual combustion proccess. The surface resistance of the bore may be affecting the state of tune.
 
softer fouling

On exceptionally hot days I use a barrel cooled after each target. Basically water pumped thru a bore guide. The barrel is definately easier to clean after doing this.
BA
 
Weather Sensitivity

Although primarily an Arrhenius equation, moisture can offset or inversely affect powder burn rates through mechanical and dimensional changes.

Ken
 
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