That's good to know. I have never had to do this yet, but wont think twice about it know that I knowI knew someone would bring that up eventually...
It's a myth, plain and simple. The amount of time you would have to tumble loaded ammo for this to happen would probably wear through the brass cases. Factory ammo is tumbled before packaging. Millions of rounds have been tumbled by reloaders before shooting. The myth is printed in various reloading manuals without proof or testing.
I do when I load with hard cast bullets, I find there is always a little bit of bullet lube residue left on the bullet that if not cleaned off tends to gum up chambers over time.



























