Yup, as long as you DO NOT motorize it, its perfectly legal. Now, i dont know if you need to register it, or maybe have a license to build firearms though.
I beleive there something about gearing it to. Maybe only like 1 turn of the crack per shot or something. Because hell, you could grab your 10 or 21 speed bicycle and hook it up and make that thing fire faster than a motor could ever turn it.
