Tumbling won't scuff off the coating if the load is compressed . . . I've heard of ammo being rendered dangerous by excessive tumbling or even being carried in the glove compartment of a Jeep for years, but these anecdotes are at least third or fourth hand . . . take them for what they're worth.J.D. Langendorph said:Lots of powder is "coated" -- especially stick powders for rifles. Tumbling scuffs off the coating. But I'd worry more about a primer going off from banging into the pointy tip of a rifle bullet.
I can't imagine any sort of logical reason why you'd want to tumble live ammo.