All manufacturing companies tumble ammo at certain stages of completion.
Non-military ammo gets tumbled more to make it look nice. Tests for change in components (powder) have proven that when it is not tumbled EXCESSIVELY, no measurable change occurs.
Think about where powder is produced, how it is loaded into canisters, how it is shipped to distributors, how it is shipped to your dealer, how your dealer displays and handles it, how you look at it & buy it & drive it home & put on your reloading bench & load into cartridges & store before use.
Then tell me how 15 minutes of vibration in a tumbler will damage the powder. Remember the statement above: "tumbled EXCESSIVELY". If you put in a tumbler and vibrate excessively, change MAY occur. If you put it in a cement mixer in a manner that allows the loaded round to slide thru the media (lots of media = nearly full), then no measurable change will occur.
But there are always stories out there that relate to how a change in components causes a KaBoom.
In reverse, I had a Squib load which caused a projectile to be stuck in bore of rifle. After waiting a large amount of time (2 minutes), I withdrew the bolt and cartridge from action. Dumping the case onto the table, it displayed a large amount of powder that did not burn. Explain to me how a small amount of powder will burn pushing projectile out into rifling, but yet the main charge looked dark and clumpy(246 grains of RL-50). These cases were not tumbled after loading as they were MATCH loadings.