The 3 D printing of a pistol was a good plot twist to a CSI NY episode not too long ago.
and no matter what you do with plastics and ceramics you can not get it to make a gun that will go through a metal detector.
The Glocks that the one Joker brought on the senate or house floor through the metal detectors went through in peices.
The frame went but the barrel, slide, springs, mags and ammo had to be brought in, in an aids breifcase that is treated like a diplomatic pouch by the capital police.
even if you could make a whole gun out of plastic, steel liners would be needed to make a chamber, and a barrel not to mention a firing pin. and cintered metal can not be used as it will not hold up the pressure and to heat it enough to make is solid metal you would put a gun in the kiln and it would come out as a blob of steel.