Current law allows the manufacturing of firearms for personal use without a background check as long as you are not a prohibited person. Some states require that you serialize them and some do not. I don't see a cause to change the law just because you can make plastic guns...as metal guns that are milled 80% complete have not been an inherent issue in society to date. Plastic is more expensive, more difficult, and less relaible and less accurate. Bullets and thier casings are still metal and will be detected by the TSA or whoever.