yes, that gun being a 1957 vintage, was made two years before the 22 magnum was even offered (made/developed 1959-60) and as 'street' noted, at that time the bores went to .224" versus the older .222"........no ,not that much ,but enough that the gun companies made TWO versions, till they offered the convertibles with the .224" barrel and S&W made their model 48 in a 22 magnum, and offered a "spare" cylinder for the Mdl 48,BUT NEVER did for their model 17 or 18's............Colt offered their Scouts and Peacemaker 22 either way,using the larger bore diameter.......................