Nothing could be as fitting for your grandsonny as this:
http://www.gunbroker.com/Auction/ViewItem.aspx?Item=539759872It practically screams "This is what my cheap prick grandfather bought me to keep me happy, after that guy with the better gun on doublegun told him to stick it". Imagine the hours of fun he will have, wishing it worked, swearing at it, and you, and wishing that he was related to someone higher up the food chain, like, maybe, I don't know, say, Goober from Mayberry.
"Grandpa cheap prick" or "Grandpa skin flint" has a nice ring to it, don't you think?
It the shoe fits....
Best,
Ted