Individuals have been working on 3D printed AR-15 lowers for a while now and one of these printed lowers was finally tested:
Earlier this year, amateur gunsmiths got together to see if they could print out some parts that could be used to construct a fully functional AR-15 semi-automatic rifle. Last weekend, a 3D-printed lower receiver was tested to failure shooting real bullets, and made it through six shots before suffering what you could legitimately call a catastrophic structural failure.
Some people are pointing at this test as a failure because the lower failed after six rounds but I see it as the dawn of a new age. Technology, as a rule, has a tendency to improve. Even though this first lower failed after six shots it proved that the concept is workable. Now that the concept has been proven viable it’s time to improve the technology. This may involve using different materials or making design changes to reinforce weak points. It is my hope that someday future generations will look back at today and say “Man, they had it hard back in the early 21st century. Did you know that most people had to buy their firearms from dedicated manufacturers? It’s crazy! I’m glad we can just print up our firearms at home, going to the store would be such a hassle.” Decentralization makes suppression impossible. If anybody can simply print a firearm at home controlling firearms becomes impossible.
along with the hard paper composite printing that Staples is introducing you could custom print your own wood-like furniture leaving just your upper assembly, trigger, and barrel to acquire.
Although if you had the money you could get an electron beam melter and make the entire thing out of titanium.