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My loading room is 10 - 12 degrees cooler in the winter than in the summer. Does temp have any impact on charge weight in cooler conditions and less humidity?

Been loading International Clays for a couple of years. This year I want to get a start earlier and stock up before our season. The drop rates are up a bit now for some reason. Same powder jug (International Clays), same machine (MEC 8567), same bushing size.

I usually drop 20.8gr for this particular load and and with everything else the same outside of the temperature and maybe a little less humidity, the drops are 21.3gr

In regards to humidity, the room is in the house and the furnace dries out the air more in the winter than the occasional AC run in the summer.

Thoughts?
 

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My loading room does not vary that such so I can't address temps. However, humidity does have an effect. We run a whole-house humidifier in the winter, so that is probably why my variances are smaller than yours. I also find that larger flake, rough edged powders like Green Dot are more susceptible to humidity variances than e3, Solo 1000, N310, WST and the like.

I tend to have new jugs of powder stored in the loading room until needed. Once opened I check the drops very carefully and adjust bushings if necessary. Once I've established the correct bushing for that load, I use it no matter when I load. The .2-.3gr drop difference caused by humidity differences does not show up on the chrono as increases in average speed or larger SDs., so I figure the "extra" weight is just water.
 

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Humidity is usually lower in the Winter, depending on where you live and what type of heating unit you have. Adding a humidifier usually helps reduce static electricity and seasonal powder weight variations. Won't totally eliminate them, but I have very little variation from the same lot of powder between winter and Summer. Without the Humidifier in the Winter, the drops can be different by up to a half grain or so.

I usually adjust the charges up or down to about where they weigh the same as before, IF there is a significant change. Little or no difference in velocity, but don't have pressure testing equipment to verify pressure. With conservative loads, a few tenths probably won't make much difference. A half a grain might make a difference with some loads. I'm usually on the light side anyway. I don't lose a lot of sleep over it, since I don't load to the max. Reloading gives me a lot of options with powders, pressures, and velocities.

Powders that are more porous might have a tendency to absorb moisture more than denser and less porous powders. I'm not sure just how much difference a miniscule amount of moisture will make.
 
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