Quoted:Both scientists felt that tumbling was a safe practice within the bounds of reason.
The Ruling
We are calling BullShooters on this one. While extended tumbling could, at some point theoretically cause a problem, a reasonable amount of tumbling to clean up loaded ammo is not dangerous.
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I cut this specific pair of sentences out of the article for a reason.
During Hurricane Irene we took about 4' of storm surge in our walk out basement. Out of all of the GI ammo cans I had stored there, one had a missing hinge pin and leaked, letting some moisture in the cans which was absorbed by the boxes in some of the factory boxed ammo and/or held agains the rounds in the a few that that had styrofoam liners. It took several days to get around to inspecting that box and by that time there was a fair amount of general ick on three boxes of ammo in that can.
They went into the tumbler and ended up being tumbled for about 48 hour total, removing the salt residue and verdigris, but not the staining itself. A couple weeks later when I expended them on the range, it functioned fine and appeared to be normal for about 100 rounds until fired one round that resulted in gas exiting the pistol - enough to feel heat and pressure on my hand, but with no damage to the FN Hi Power I was shooting it in. I recovered and examined the case and discovered this:
I stopped using ammo from those boxes, but when I policed my brass at the end of the session, I discovered 4 more cases that looked just like it.
This was factory ammo in new brass and the failures occurred in portions of the case that were not affected by any corrosion.
What's left here for probable causes is the excessive tumbling done to clean the ammo up. In this case, 48 hours of tumbling resulted in about 5% of the ammo having enough pressure to cause the case to fail at the unsupported section of the feed ramp. I have no idea what powder was used in the ammo, but it apparently did not hold up well to that amount of tumbling.
Personally, I don't tumble live ammo anymore, based on my experience, rather than what I read on the internet.
If I were to tumble ammo for some reason in the future I'd limit it to just a couple hours at most.