Actually, old defunct shotgun barrels are easily found, at gunshows, antique shops, or even some garbage dumps. That solves the pressure problem. The transplanted trigger mechanism from the stapler - good idea. Weak point: the lockup. Wouldn't ever shoot it from the shoulder, because that'd put the blowup right under your nose. Abusive comment hidden. (Show it anyway.)
A lot of time on their hands, when they weren't killing/dying for their country.
Nice to see a picture of it.
Let me suggest 'The Space Merchants' by Pohl&Kornbluth.
And who can forget Bill Cosby's bit about 'The Chicken Heart that Ate Chicago'? What do you suppose all that heart was supposed to be for?