[eno_]

I'm not a gunsmith, but I'd imagine it would be possible to fabrcate a barrel out of ceramic, reinforced with carbon-fiber-epoxy if need be.

Googling around I fnd there are ceramic/steel barrels. I see not reason the outside of the barrel would have to be steel. I also found a spear gun (for spear fishing) with a ceramic/carbon-fiber barrel, but I have no idea how spearguns are propelled, so I don't know if there are order-of-magnitude differences between spearguns and normal firearms.

[E. Pluribus Unum]

I'm not a gunsmith, but I'd imagine it would be possible to fabrcate a barrel out of ceramic, reinforced with carbon-fiber-epoxy if need be.

I guarantee you such a barrel would be radio-opaque. It would show up on an x-ray.