[jyl]

I don't see why one couldn't make a completely non-metal repeating pistol.

There's been work on ceramic lined gun barrels, it is quite feasible. To reinforce barrel/chamber for firing pressure, there are extremely strong plastics. Springs could be plastic, rubber, or even air/gas springs. Would need custom ammunition of course, caseless or plastic like a shotgun shell.

But what is the point? Airport security systems see all dense things, not merely metal, and don't need a gun to hijack a plane.