Congress Extends Ban on Plastic Firearms, But What About 3-D Printed Guns?

The New York Times reports:

The House voted on Tuesday to extend a law banning firearms that can pass undetected through airport X-ray machines, but left out provisions that law enforcement officials say are necessary to combat the growing threat of guns made with 3-D printers. 

. . .

As the law is currently written, manufacturers of 3-D printed guns are only required to make their firearms detectable to security screeners in some way, usually by including some form of metal. But some designers have made that metal piece nonfunctional and easily removable. 

To close the loophole in the current law, the changes proposed by Democrats would require that an essential, nondetachable piece of the gun be made of a sufficient quantity of metal to be picked up in a security screening.

I think that the Democrats' proposal that an essential piece of the gun be made of metal is a good one and would be an important legislative step towards preventing misuse of 3-D printed firearms.  

And if opponents of the ban are correct in arguing that that "3-D printed guns are expensive to make and unreliable to fire," I am not sure if this means that the guns are "not worth regulating". The upshot of their claim instead seems to be that any additional regulation would put no meaningful burden on those who print firearms -- since those firearms are either not practical, or not being printed in the first place.