Most of the '3d printed' guns out there in the 2a community, and all the ones that actually work, require some kind of metal barrel, which might be a pipe, rifled or not.

What they actually hate is people who buy bags of glock parts from ebay (contains everything but the frame) and then print the frame. The frame being the handle part, everything below the slide but none of the internals. That's the legal 'gun' when it comes to most glocks and clones. The new ruger rmx, a newer glock clone, is different, the firing group (trigger and all the associated bits there) is the serialized part. The frame is, of course, very easy to print.

All the regulations around firearms are super fucking stupid, the way they classify different parts and try and make them illegal. Like.. in a lot of states if you have a rifle (ar or otherwise), you are not allowed to have a vertical foregrip for stabalization. However if your foregrip is like 5 degrees off pure vertical... legal.

This 3d printer 'ban' is unenforcable, it's a fucking tool, you can build anything with tools. Sure it's easier and takes less skill to download a glock 19 frame model off the internet and hit print, but there is, apparently, a lot of work that goes into making the gun work with that frame well enough for the gun to actually cycle.