Senator Blumenthal of Connecticut will be introducing a bill to require background checks on all ammunition purchases. This will help address a significant weakness in the regulation of arms, but this bill doesn't go far enough. Blumenthal's bill only covers cartridges, or factory ammunition. Many firearms owners load their own ammunition. They purchase the bullets, cases, primers, and powder, then use a press to assemble these individual components.
The assault weapons bills that are being introduced around the country have a similar weakness. An AR15 can be made in one's garage. These firearms do not contain a serial number, and are not registered.
Only the lower receiver on a complete AR15 is registered. All the other components that make up the completed rifle are not registered. A large market exists that sells high quality components that require little, or no gunsmithing to fully assemble an AR15. It is also possible to purchase 80% complete lower receivers that have no serial numbers, and are not registered. After some "do it yourself" work, you can have a fully functional, unregistered AR15.
Use your 3D printer to make some high capacity magazines, and you are good to go.
I suppose that if it was found out that al queda was doing these things rather than "law abiding citizens", someone might show some concern.
Do it yourself AR15.
CNC maching an AR15 lower receiver.
3D printed magazine.
Handloading at home.