Humidity and Gunpowder Volume.

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gonoles_1980

gonoles_1980

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I use my historical measured VMD as a second check when I load my powder. Normally when I load 3.4 grains of Bullseye for my 38spl, the VMD on my Lee Power Measure is between .416 and .419. Today, it's very humid, and it's measuring .433.

I double checked the scale with check weights, and the scale seems to be measuring fine. I can put 3.5 grain scale weights and the scale shows it's weight about .1 grain heavy, which is what I want since the scale is set at 3.4 grain.

I keep my gunpowder stored inside under air-conditioning, I reload on the screened in back porch, which is where it's humid and not air-conditioned.

Thoughts?
 
Last edited:
You might be better off storing your powder in the environment that you load in. I'm thinking that bringing it from a cool dry area to a humid area would promote condensation/water absorption.

Dave
 
The VMD is only useful for estimating the VMD of your particular powder at any given time and place, humidity, phase of the Moon etc., and if using a Lee VMD metering on a PPM. It gets you close when adjusting the metering rod, you still have to weigh the drop.

It is essentially useless if you weigh your powder on a Accurate scale.
A grain is a grain is a grain.

https://leeprecision.com/cgi-data/instruct/AP1704.pdf

JMHO
 
The difference between .433 and .416 is 4% or 0.14 grains @ 3.4g. Add scale error and you are in the noise.

Good enough.
 
When I resume reloading the same thing again I dump the propellant in and run the measure 20 times to settle things. Then I run out 10 drops and weigh them. they should equal 10X the weight I want, if not I will run the 10 drops again and weigh those. If still off I will adjust the measure. Repeat test as needed and load when things are settled and accurate to my liking. Yes volume will change with humidity but keeping your propellant in an air tight container and closing it tightly after each use seems to minimize the problem for me.
 
Thanks guys, it was the first time I had seen a larger difference like that with Bullseye on this particular load. I use the VMD as a secondary check only.

My process:

Zero the scale
Calibrate weight at the nearest .5 grains to my target load weight (e.g. 3.5g for 3.4g load).
If I need to re-calibrate after check weights, I recheck zero again, then redo the 3.5 again, repeat until no re-calibration needed (very seldom need to do this).
Set the VMD on the metering rod on the thrower to historically measured average VMD
Throw the weight
Weigh the throw with the scale set at my desired weight
Adjustments on metering rod should be minor to get desired weight - if not, I review the entire process.

Probably overkill, but it makes me feel better that I have doubled checked things.
 
FROGO207 said:
When I resume reloading the same thing again I dump the propellant in and run the measure 20 times to settle things. Then I run out 10 drops and weigh them. they should equal 10X the weight I want, if not I will run the 10 drops again and weigh those. If still off I will adjust the measure. Repeat test as needed and load when things are settled and accurate to my liking. Yes volume will change with humidity but keeping your propellant in an air tight container and closing it tightly after each use seems to minimize the problem for me.
Click to expand...

IMO, Weighing the "average" is not really a statistically valid way of determining powder measure in teeny tiny grains. It is just that, an average.

Maybe one drop was over and another was under?? The average may be correct, but on or more individual charges may be off by a lot.

Weigh each and every one of the Ten powder drops and you have repeatability.
 
I agree with RULE
set powder measure based on individual drops - verified with a good scale
once you can get 10 individual throws consistently your good to go
averages are for approximating
 
Yeah maybe I should be more clear in that I have used the Ideal 55 so much that I know which propellants will meter with little variation and just use the average. The others like 700X and such, I use custom scoops I make to be sure the amount is what I need. I just verify them at the start of each session as long as it is the same lot of propellant. The scoops will not change throughout a loading session, but I have had an adjustable one change though..
 
Over time, I find that I have to tweak my powder measures to throw the desired charges at each loading session. All of my powder measures have micrometer adjusters. I record the setting at each loading session so I know what it was set at at for the next reloading session.

Best that I can figure, the moisture content of the powder changes a bit from one loading session to the next but I cannot verify that for sure. Bottom line, I adjust/tweak the powder measure for the charge weight that I want. The recorded setting that I have gets me in the ball park.

P.S., when I was gainfully employed in business, I worked for a paper company and moisture content of the paper was always a consideration for figuring quality and paper content of the sheet. Old habits die hard sometimes.:)
 
FROGO207 said:
Yeah maybe I should be more clear in that I have used the Ideal 55 so much that I know which propellants will meter with little variation and just use the average. The others like 700X and such, I use custom scoops I make to be sure the amount is what I need. I just verify them at the start of each session as long as it is the same lot of propellant. The scoops will not change throughout a loading session, but I have had an adjustable one change though..
Click to expand...

Only if you scoop or dip correctly:)

One must use a straight end and level off each scoop to ensure perfect baking of each loaf.:):)
 
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