Mulely... for my part here is my explanation. BH-209 is a Smokeless Progressive burning powder engineered to mimick BP in pressure and volume measure and therefore can be listed as a black powder sub and by doing that bypass some of the federal regulations pertaining to smokeless powder. And of course it allows them then to market the powder as a SUB...

It is not a really good smokeless powder at that but it is great for a ML. One of the problems they had was to make it bulky enough that it would meter in a volume measure along with the regular BP products.

BH does contain a small amount of potassium nitrate and sulphur which does effect how the powder operates but it also makes it a bit more of a challenge to clean up than regular smokeless powders.