Let me help out.
If you put stick powder in a blender, to exacerbate the vibration type effect, what will happen is that your rifle powder will turn into a pistol powder and burn DRAMATICALLY faster. This is a fact, not a myth.
But tumbling is super less than blender. But stick rubbing against each other, probably has small impact. Small. IN confined space. under extreme vibration. Which is way different than container rocking around in a truck.
This is tested and proven. (Blender that is)
as far as cleaning brass. Here is a proven method you may like. Pretty standard, just add ShineBright.
http://www.natoreloading.com/cleanbrass/