I'm guessing that the fools who wrote these laws never even took it into consideration. I you mentioned .50 Beowulf to them, their response would be "Fifty-wha?" So this is something the law was never designed to even address and as such becomes a gray-area. Perhaps not necessarily illegal but something that can bite you in the ass if some prosecutor decides he doesn't like you.
This is what happens when you put gun regulation in the hands of people who know nothing about guns.