Never....Seems to me that was a benefit of a brass barrel and not recommended from the factory.OK, that isn't exactly true, when I first get an old gun of unknown origin, I pull a WD-40 or Goo-Gone soaked patch threw it with a stringI then break 5 or 6 Q-tips in half, load like a pellet, and shoot those with a pump or two.But never do I run a brush or rod down the Bronze barrel.