Originally Posted by Loren Pechtel

Where have been for the last two years?

There's a plastic pistol out there already, admittedly a bit unreliable and certainly not good for more than a few shots. The only metal part is a common nail.

It fires a standard metal-cased bullet, though.

While I haven't heard of it being done one could no doubt make a muzzleloader version that omitted the metal of the casing. Also, I'm sure there are chemical means of firing it that wouldn't require a metal part. You're not going to be able to get around a metal bullet, though.