Originally Posted by Woodhits
I did an article on this many years ago. Here was the gist:

I spoke to the Chief Ballistic Scientist at Hornady Manufacturing and the Head Ballistician at Hodgdon Powder and asked for their professional opinions. Both agreed that this is a myth devoid of empirical data.

"Powder is hard, it doesn’t change shape from any reasonable amount of vibration,” said Hornady’s Dave Emary. “This notion that you can wear deterrent off of the surface of the powder is a myth, it is impregnated into the powder grains. You can’t knock this stuff off."

Both scientists felt that tumbling was a safe practice within the bounds of reason.
excellent ..
now I guess the real question is can a primer be set off accidentally by vibration