Humidity level can affect powder burn rate.

[ShtrRdy]

There have been times over the years that I came up with a load that worked well and then when I loaded another batch of cartridges the load didn't work as well. There are multiple things that can cause such a result but I would like to point out that the amount of humidity in the air can change the burn rate of the powder. Here is a link to a paper describing some findings:

https://chronoplotter.com/2021/08/19/how-does-humidity-affect-powder/

I've been using humidity control packets in my powder containers. Specifically the Boveda 49% humidity control packs.

 

[Alan]

Yeah, humidity can sneak up on you and it is not always obvious, but it explains those “same load, different result” moments. Thanks for sharing the research

 

[Trigga]

Interesting point, consistency matters. I’ve seen more variation from temperature swings than humidity, personally

 

[Kora]

After some weird velocity swings one summer, I started storing H4350 inside ammo cans with Boveda packs.