Had several people ask about this in a previous post, so I thought I'd disclose the limited knowledge I have on this thing.
He is a machinist, so it was a simple project for him. It's just a large diameter piece of cylindrical aluminum stock, bored to accept a golf ball, and drilled and tapped to thread onto the muzzle, I believe. Nothing really elaborate at all. He lives quite a ways away from me, but I'll try to get pics, if possible. Then I'll have to try to figure out how to post them!
What I don't know (among other things HAHA!) is how readily available blanks are, or where he got them, but he has a BUNCH! It is a RIOT to play with, and I suppose you could adapt the launcher to work with tennis balls by making it on a larger scale.
That's about all I know, which ain't much!