Just look up 3D printing technology. Think about a ink-jet printer that prints out something 3D with ABS plastic. So, with such a thing you could "print" out a gun. The technology is in its infancy, and although there was a guy who got a 3D printed AR receiver to fire a couple of rounds before it all fell apart; it's really not viable for the firearms industry at this time. But the technology will grow; who knows. In 15 years we may be sitting around listening to everyone bitch about the quality of 3D printed parts, longing for the days of MIM.
Times are a changing, and there will come a point in the not too distant future that the ONLY way to control guns is through ammo. We need to be very diligent about ammo bans. Fortunately, I think we have a good deal of protection for ammo bans under the Heller decision, but I’d like to see something specifically defined in SCOTUS case law for ammo.