Possession- 4. Law. actual holding or occupancy, either with or without rights of ownership.
http://dictionary.reference.com/browse/possession
So in any State that limits where possessing a set amount of Black Powder, say 5/lbs., carrying around 5/lbs. would be legal at the range(at one time). But if you left 5/lbs. of the 10/lbs. home, that you ordered and was transported under a hazmat permit issued under Federal law, I'd say you'd be within' the State law by the Legal definition of Possession.
SG