My guess is, the article in PS read .17-221 or .17 MachIV, which the reader mistakenly read as .17-223 or .17 MachIV. At any rate, .17 Fireball brass is now readily available (Just took delivery of 300 cases from Midway), so that's the route I'd suggest he take.

I also don't believe it's a good idea to "load her up and let her rip", as too much bad $#@! can happen!