The reloading manuals all tell you not to do it, tumbling loaded ammunition. The reason is pretty clear – the vibration could cause the powder grains to break, or damage the coating, both of which would increase the burn rate and so result in higher (and unpredictable) pressures. Obvious really, and so I never have.
But just recently I met a man who has loaded millions of rounds, and who tumbles them all, to clean off lube and remove any contaminants before packaging. With that volume of evidence, I thought it was time to do a bit more research on this questions.
Of course, I discovered the Internet has no shortage of views on the topic! Some referred to scientific studies, but without citations. Others described rifles blowing up as a result of tumbled ammunition.
Some commentators made observations that had not occurred to me before. About ammunition bounced around in railway boxcars and Army trucks, and of ammunition carried in airplanes and exposed to constant engine vibration. All of which got me thinking that maybe there were two sides to this question.
Maybe the manufacturers are pursuing a counsel of perfection, to remove any risk of litigation on the point. And they may have a point – one anecdote I found referred to loaded ammunition being tumbled for 24 hours and blowing up a rifle! That cannot be a sensible thing to do, whatever your views on tumbling loaded ammunition.
It would be useful if I could tumble loaded ammunition to remove the lube. The alternative is to tumble the de-primed and re-sized cases before loading, which always results in media blocking some of the flash-holes. Or I have to wipe off the lube by hand once the round is complete, which is a boring process.
If the practical experience of millions of rounds was not enough to convince me, I consulted Dillon Precision on the subject. They responded (very quickly) that “We tumble loaded ammo in plain corncob with a couple of tablespoons of alcohol added for about ten to 15 minutes. This won’t damage powder or alter the burning rate at all.”
And that seems to be the key. Tumble the loaded ammunition just for a few minutes – not to polish the brass, but just to remove any contaminates.
I did find a reference to some empirical testing by Geoff Beneze, who apparently tumbled loaded rounds for weeks to see if it affected the powder. He concluded it did not. It is a shame all the testing results are not available on-line but it is interesting nonetheless.
So I have decided to change my approach, and tumble the completed rounds in line with the advice from Dillon. Just enough to clean them – and remember to set a timer!
