I had a M17 and wanted a 22 mag revolver. M48 S&W’s are quite rare here and I went a slightly different route. Eventually I found a smith locally that had a spare 22LR cylinder. He also happened to be a S&W trained armourer. I had him ream out the spare 22 LR cylinder to 22 Mag and fit the new cylinder to the M17 frame. This way I had a convertible M17. The difference between the M48 and the M17/18 is the barrel diameter, 0.224 vs 0.222.
As a bonus the accuracy of the 22 Mag cylinder was better than the 22 LR cylinder, which I attributed to the tighter barrel specs. There was one problem though, the higher pressure 22 Mag shells pushed the firing pin bushing back slightly into the frame. The 22 Mag cases were ballooning out slightly at the rear making the cylinder sticky to rotate. Anyhow, the smith made a new, slightly longer firing pin bushing and fitted it precisely and it has worked perfectly since.
