Originally Posted by JimN
Money talks- if someone has a ton of cash, and some gangs do, they can find someone with a 3d printer and the ability/desire to make these for whoever pays.
...but you can still only make an empty plastic lower receiver that has to be built and has a very limited lifespan - buy the upper, assemble everything and then what? Where is your advantage to being able to do this? It would just be easier to go and buy a complete AR that will fire thousands and thousands of rounds reliably, then to go through all of that hassle to fire a couple hundred (maybe) before it breaks. If you are worried about trace-ability - then buy an aluminum 80% lower (which is not considered a gun or serialized either), finish the machining and build a regular AR that has the reliability and is not traceable. I don't see where the 3-D printing is a realistically viable and practical option just to get around Big Brother - even for someone with a ton of cash. It is more of a novelty and a challenge to do it than anything to practically worry about.