3D-printed full-auto bullpup 'ghost guns' can now be made for a couple of hundred dollars — designs have evolved dramatically outside the U.S.

https://www.tomshardware.com/3d-printing/3d-printed-ghost-gun-designs-have-evolved-dramatically-outside-the-u-s-full-auto-bullpups-can-now-be-made-for-a-couple-hundred-dollars