From Carlito's Way:

> Out come the zip guns. Homemade gun. You pull the hook back, catch that bullet square, ping. Hit you in the head, man, you got serious problems.

Yes and the response is telling you that you can build something orders of magnitude more sophisticated without any trouble. The point is, the firearm is not the tube the projectile comes out of. Firearm is closely defined and not intuitive to the general public.