Say you buy a 4 lb. (some pistol powder) or 8 lb. (some rifle powder) jug and take it home.
It's been handled at the manufacturer, it's been handled when loaded/unloaded for shipment to a dealer, it was handled at the dealer, it's been transported here/there/yonder during all this. If bought at a gun show, it might have several trips/transports under it's belt.
What does handling, bumping, bouncing, transporting do? It causes particles of different sizes to separate into "layers" top to bottom in the container. If there are differences in the powder flake/granule size some separation will occur. Gravity, particle size, particle surface and shape characteristic affect how much separation occurs and how fast it occurs.
I used to work in a manufacturing facility that made/used flakes of material as a raw material for other processes and used chips of varying sizes as raw material for other processes. Particle separation is a fact (based on size, shape, handling, surface/shape, etc.)
So, has anyone else noticed an issue with this in a big jug of powder over time? I wondered if that was what was going on when I'd set my powder measure up for a certain weight and load a few hundred rounds only to find out as I worked my way through the jug I'd have to use a different powder measure setting as I worked the powder off the top and got down into the middle/bottom of the jug.
I've wondered if I should be setting my jugs down on the floor and rolling them back and forth before pouring the hopper full.
Just curious what the other reloaders here think about this.