During the era involved with production of the Ruger Mark II pistols, there's one prototype pistol that didn't quite work out. Ruger produced at least one blued carbon steel, 8-inch fluted Hunter style barrel Mark II in the .17 HM2 caliber. Unfortunately, the pistol was unable to cope with the "recoil impulse energy" involved with the .17 Mach II cartridge: The above page is from one of the "slick" magazines that covered this prototype pistol, but if you look closely the ammunition depicted will not fit the pistol. Hornady didn't have any of the .17 Mach II ammunition available at the time this article was printed, so the author instead, substituted .17 HMR. The original plan for production was to make these guns from stainless steel, but the failure to function without damage, scrapped those plans. Too bad, it would have been a simple matter to abandon the .17 Mach II cartridge and go with .22 Long Rifle. I certainly would have had one in my safe, right now.