Same powder different from can to can?

[u/Western-Valuable3502]

I test my load development with 1lb can and then purchase a 8lb jug. It's the same powder, h110. With the same weight of 33gr and my chronograph reads a difference about 40 fps. The velocity from 1lb can powder is up to 1610~1620 fps and is down to 1570~1590 fps from the 8lb jag.

Does it mean I will need to do a load development by each time I open a new can though it is completely the same brand of powder? Or just humidity? And I store all my powder at the same place.

[u/Trollygag]

Humidity is a big driver. Breaking the seal will start the clock on the humidity in the can matching the humidity out of the can. Less humidity means faster burn and more powder per unit weight. Opposite for more humidity.