I’m looking into adding a 22 mag cylinder to my 17-2 . My question is are the 48 cylinder the same dimensions as the 17’s? For example the 6shot m648 and say 48-7 the same size as older 48’s? I know some cylinder seem to fit right in and some need a gunsmith’s touch , what say yah’s are they dimensionally similar.

I fit a new 648 cylinder to my vintage model 17-2 a couple of years ago. The fitment of the new cylinder, purchased at Numrich, was very easy. The cylinders were remarkably the same, despite their age difference of fifty plus years.

The only major work was hand cutting the new ratchets/extractor to work with the model 17 hand. Due to the redesign of the extractor stem, the extractors cannot be shared.

Looks a little strange with the magnum cylinder installed, but the gun works perfectly with either cylinder. In my case, changing calibers only requires switching the cylinders, and moving over the center pin, center pin spring, extractor spring and extractor rod.

Some additional info from the forum here:

Your thoughts, .22 to .22mag

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Ret. LE, FA Instr, S&W Armorer