Via an email from Paul K. we have instructions on how to make a working gun out of paper. I have duplicated the instructions here for archival purposes.
I really, really, have serious concerns about using one of these. I can see where the radial strength might be adequate when using a small gauge shotshell but the recoil could still be a problem. There is no breachface and stock to prevent the shot shell from pushing the nail (firing pin) and perhaps the case-head into/through your hand.
Use at your own risk and remember that the extent of my obligation should this result in you or a friend of yours dying an unnatural death is to nominate you for a Darwin Award. If, and only if, I am in a generous mood when I learn of your date with fate.