3D printing could nullify magazine bans.

You may have heard of the latest advances in the field of 3D printing. If not, here is the basic rundown: 3D printers are machines that function like a CNC machine for milling metal or wood. However, instead of milling out the object from a solid piece of material, 3D printers form the object from scratch by melting plastic, and "printing" a 3D object. By printing separate parts, one can produce entire assemblies of parts.

There has been increased interest in 3D printing in the firearm community, especially because of one organization known as Defense Distributed, or the Wiki Weapon project. The ultimate goal of this project is to produce a fully functioning AR-15 rifle from 3D printed parts. Defense Distributed has already succeeded in producing a functioning AR lower, but the component broke after several shots, due to the weak plastic it was constructed from. While current hobbyist printers are restricted to plastics, we can assume that as this technology matures, we will begin to see printers capable of constructing significantly stronger plastic parts, or even printing metal parts.

While the printed AR may have been failure (if you want to look at it that way), the Wiki Weapon project has successfully produced a completely printed 30-round AR magazine, which survived a full unload of its ammunition.

If this technology further matures and becomes more and more affordable, magazine and gun bans may become completely useless. Defense Distributed used a very expensive high-quality printer to produce the AR mag, but they are currently working on a design that can be produced on cheaper hobbyist/in-home printers.

Citations:
http://hackaday.com/2013/01/15/print-your-own-30-round-ar15-magazine/