>"AK-47: You might have trouble hitting the side of a barn from inside,
>but by God when you pull the trigger it goes bang." Also, I'm pretty
>sure that you could build one in a cave with a box of scraps, even
>without being tony stark.

Indeed, there are gunsmiths in the highlands of Pakistan who regularly do just that: http://en.wikipedia.org/wiki/Khyber_Pass_Copy.

(Well, probably not in a cave per se, unless they're hiding from drone strikes.)