BH209 is basically much cleaner due to it being a progressive smokeless black powder substitute. However it needs to be cleaned with a conventional petroleum base smokeless powder solvent. There can be some hard fouling in the nipple hole of inline rifle breech plugs than can require using a drill bit to remove by hand, as well as a fair amount of blow back residue in some types of inline actions. But there are ways to tighten up the fit between the 209 primer and receiver, and also the fit of the 209 primer within the nipple that can greatly reduce the blow back residue. But generally barrel swabbing is not needed for many shots when loading tight sabots which is why it's considered to be the cleanest powder.
Last edited by arcticap; August 10, 2012 at 11:06 AM.