Somebody went out and 3D printed an AR-15 receiver. Out of regular plastic, not even polymers used in most firearms or even something like GRP (glass reinforced plastic.)
Best of luck to them for future versions. I for one would like to see this concept succeed. As far as something like a defense contract goes, if they could print out weapon designs in metal or good polymers on a 3D printer, a lot of milling and machining steps could be eliminated from the process, which means that the cost of arms for militaries will decrease, which is good for their budget, good for the taxpayers, and if the weapons work just as well, also good for the soldiers.
As far as the civilian market goes, I predict that acceptance will be far more limited. Mostly, I predict 3D printed guns will be used to show why gun control is not really a successful idea. Secondly, when you tell an American they can’t do or have something, they tend to want it more or try to find a way to do so regardless that exploits a loophole. Most 3D printed civilian arms will likely be people who want to demonstrate the issue with gun control, or just to rub it in more that they, in fact, can go build firearms, and instead of machine tools, they will just go print one out.
I doubt they will see much use beyond being used to make a point. As it stands, people will spend several thousand dollars on a hand made shotgun because it is hand made. Sure, a machine can do a more accurate and more consistent job, but while hand made guns hold appeal and mass produced guns still have appeal, printed guns will most likely not really be accepted by the average shooter.
However, As part of those above predictions, I would say that 3D printed arms would be accepted by the budget shooter. If you could get a pistol of reasonable quality for less than a Hi-Point because it is 3D printed and thus even cheaper to make, what person who has a major budget and wants a gun wouldn’t buy that?