The devil is in the detail also. Black powder is already regulated to such an extent that it is becoming difficult to buy any quantity of it without alarming some Fed idiot. Control of the shotgun ammunition will also be part of it, thereby eliminating any threat of a tactical shotgun.
Technology allows an alternative possibility to roll your own.
http://docs.lib.purdue.edu/dissertations/AAI1469923/
http://sbirsource.com/sbir/awards/13080-chemically-driven-hydrogen-gun
http://en.wikipedia.org/wiki/Nano-thermite
https://en.wikipedia.org/wiki/Potassium_permanganate