Howdy,
Didn't AMT make a .22 Magnum Automag? From what I understand, it is quite difficult to build a reliable blowback pistol for a high-energy cartridge that can work reliably with many different makes of ammunition. It was once thought that a conversion of a 10-22 to .17 Mach II would be as simple as replacing the barrel, but when recoil velocity, etc were taken into account, it wasn't an easy job at all.
I think the only workable pistol in .22 Magnum would be a delayed blowback or gas-piston design.
Bitterroot Bob