Those don't generally have any ferrous components.

No idea. I only replied to the guy saying that "metal detectors stop weapons". Which is false.

The evidence is in US law. Because they would be undetectable, 3d printed guns are required to have some metal inserted into it to be legal (https://en.wikipedia.org/wiki/3D-printed_firearm#United_Stat...). I think a guy who can 3d print a gun and wants to bring it onto a plane could probably skip that step;)