Check out this link on youtube it is eye opening and very interesting. Loophole? You decide. Check youtube and type 'printed guns' in the search field.

It's not really a loophole, it's perfectly legal to make your own firearms.  (Subject to certain restrictions)  All this does is remove the obstacle of needing to be a competent machinist in order to do so.  What I've been saying for years is that gun control is a joke because guns are relatively simple machines that humans can build with a minimum of skill or effort.  A simple 12-gauge zip gun can be built for around $25 with basic plumbing supplies from Home Depot or Lowe's.  Sure, it's crude, but it would be enough to knock over most convenience stores or intimidate a mugging or rape victim into compliance.  This just further drives home the point that human knowledge, once obtained, is a genie that can never be put back.  Look at nuclear weapons.  We developed those under the highest possible levels of secrecy, and within a few decades they were in the arsenals of a whole bunch of countries that we absolutely didn't want to have them.