There are a couple fairly recent designs for 3D printed guns that are useful weapons, certainly better than the pipe-wood-and-nail arrangement. For example, the Washbear PM522 and the Liberator 12K shotgun.
But as another poster pointed out, ammunition is a completely different matter and is really the gating factor in all of this.
But as another poster pointed out, ammunition is a completely different matter and is really the gating factor in all of this.