Originally Posted by Trental
Do some Google searches and you should find some guys that have already done the testing. I would post some links but I am at the range right now.
Ditto on this one, there's a fellow over on AR15.com who did extensive testing on tumbling live ammo. In long term tumbling, "something more than 24hrs" There was only the slightest surface change to powder granuals "viewable with a microscope" and it resulted in no or very little measure in performance.
Some people say don't do this or that sometimes just because they want to have an oppinion. You could always tumble a few loaded rounds for 24 then 48hrs to find out just how long it does take to actually damage a powder granual.