Can thrown charges from a fixed metering device change a few tenths with higher temps and humidity.......Thanks.......2#

I suppose you mean a few tenths of a grain, i.e., weight, in which case yes, it may vary a bit with variations in humidity, but, apart from convenience, most of the point of measuring charges volumetricaly rather than by weight is to eliminate just this variable. Once you've established your optimum charge volume, you can forget the slight environmentally caused differences in weight, and you won't be using any more or less actual powder. Or, or so I understand... If i'm mistaken about this, I'm sure others will be quick to point it out.

I always weigh what my press is throwing at the start of every loading session and adjust accordingly.

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Where we go one, we go all

Since the humidity is water, the weight difference would give you less powder and more water for the same weight in a low humidity environment.

That means you'll never get an overload of powder in higher humidity situations, provided the weight is an acceptable one to start with.

Bob,

There's just a little bit of water involved in high humidity conditions. I think we had a member on Handloads.com that checked at various humidity levels (he works at a lab facility) and the weight difference was very small. That was several years ago, so I can't give you exact numbers.

A 1/10th grain weight of powder is a really small amout, just a couple of flakes of flake powder and only a few pieces of ball powder. Much depends upon the size of he flakes and how dense or heavy they are.

Temperature can degrade powder in storage and loaded ammunition. With temperature changes and enough humidity moisture can condense out of the air. However I've never read of any hydroscopic properties of smokeless powder saying it will absorb water from the air. I don't believe there's any significant change in powder weight due to ambient temperature and humidity alone though I could be wrong. it would take a good series of tests under controled conditions to determine if there is any significant affect.

IMO the variation one sees from one session to another is due to powder settling in the measure under vibration during use or over time if one leaves the measure full of powder.

Powder generally isn't totally uniform in size or shape so slight variation in charge weights are somewhat to be expected from volume throw to throw. This, among other factors is why we see variation in velocities from round to round.

Temp no, humidity yes, BUT the effects are too small to consider unless you have been storing the powder incorrectly. Internal ballistics are VERY complicated and non-intuitive. Main thing is to take care of your scales and measures and check them against each other and a standard periodically.

The density altitude (temp, humidity, pressure) when you shoot the rifle round has a large effect on the EXTERNAL ballistics of the bullets, which is why an elk rifle has to be re-sighted for high altitude.

For defensive handguns, the effects are negligible.

Most reloading charts are based on + or - .1 grains. Very few powder measures will throw exactly the same weight every time. The difference is not measurable on the target.

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H Richard
SWCA1967 SWHF244

“Internal ballistics are VERY complicated and non-intuitive.”------ If anything an understatement!

I would think that when splitting these hairs, the powder measure chamber would also be expanding and contracting with temperature at a greater rate than the powder.
Since I don’t think that powder is very hydroscopic, and it lives in a closed container, is transported in a mass to another closed container (powder measure) that we give it much exposure to humidity.
I agree with the idea of using weight as a constant, partially as its the way the data is spelled out.
I keep my shop at 37-38% RH but mostly to avoid rust.

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Ipsis Rebus Dictantitbus

I move a Lee Auto Disk Measure back an forth between a 650 and a Classic Turret. I ran into inconsistencies (as much as .2gr under) with a Micro Disk that I reamed to give me just 3gn of 231 under 148gn wadcutters. Apparently it's not an enthalpy issue. It sounds like it's time to replace, have dropped countless charges in five or six handgun calibers, doesn't owe me a thing, guess we all get tired and worn eventually. Thanks for the responces........2#

twopoundpull My objection to the auto disk is the lack of flexibility.
Using a measure with a variable chamber I can set it where I want it. Generally, when I go back to a recorded setting on my measure I find it a wee bit off using a carefully calibrated scale. A tiny turn and a slightly different setting and I am back where I want to be.

Did temperature cause the powder to expand faster than the chamber? Or the humidly expand the powder? Was it the phase of the moon influencing the force of gravity? Or maybe gremlins, who knows? I know a twitch of the knob will set it right..

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Ipsis Rebus Dictantitbus

Hello oldRoger, I do use a variable chamber Dillon and RCBS Uniflow for rifle and handgun hunting reloading. For indoor range use I found the Auto Disk handy when switching from 38 to 357 to 41 to 44 to 45LC to 45ACP, with different paper and steel plate rounds mixed in. I have pet loads developed using a certain disk/cavity on the Lee measure. I was running into problems when the disk that dropped 3.0gn's started shorting down to 2.7-2.8, that's Squib territory with 231 under a 38 wadcutter in some of my longer tubed handguns. I'm 6'3" 210lb big hands and arms, I still enjoy "almost" being able to see the bullet slowly travel down range......But it has to make it out of the barrel.......2#