If you want a gun you can use more than a couple times need metals. However if the goal is one shot plastic is good enough. Even plastic bullets will work - not well, but one well placed/timed shot is all we are talking about.

Not in the context of someone smuggling a weapon through a security checkpoint. At least not unless they're certain that it's small enough not to trigger the detector.

That said I will note that it is generally illegal to possess such nonferrous weapons regardless of circumstance.