You would only make the lower with a 3d printer. Here is an example: http://hackaday.com/2012/07/26/3d-printed-ar-15-lower-works/ http://hackaday.com/2012/07/2

You would only make the lower with a 3d printer. Here is an example: http://hackaday.com/2012/07/26/3d-printed-ar-15-lower-works/ http://hackaday.com/2012/07/26/3d-printed-ar-15-lower-works/ You would still want metal for the barrel (of course) and trigger assembly. Pretty much anything taht routes hot gases or contains explosions has to be fabbed from steel. The lower is only a mount point for some comopnents and a guide for the magazine.