[Shoney]

As long as you don't run it for an excessive amount of time (days), it is perfectly safe. For years commercial reloaders have used cement mixers filled with shreded newspaper to tumble loaded rounds.

I have a friend who is a farmer/rancher in Montana. We worked up a load for his 25-06 about 10 years ago. That coyote rifle, along with two 50 round plastic cartridge cases have ridden in the cab of his last 3 pickups. Each pickup had well over 100,000 miles on gravel roads, open prairie, and across fields. Those bumpy conditions have worn holes in the plastic top above the last 30 or so rounds. They are still very accurate, with no pressure signs.

If any tumbler can even come close to those vibratory conditions over that length of time, I am yet to be aware of it. So I feel very comfortable running my loaded rounds in my vibratory tumbler for about 20 min to get the final finish.