From the SCSW:
M 649:
2 1/8 inch 357 Magnum Full Lug Barrel 1996 - 1999
1 7/8 inch .38 Special only 1997 - 98 Discontinued 1999
M 649-3
This is a little harder to understand but, apparently, 1997 saw a deletion of .357 Magnum and a reintroduction in .38 Spl +P. . 2003 it says .38 Special only.
Pages 318-319 SCSW
Since a J-frame in .357 Magnum answers a question nobody really asked, or, nobody should have asked, discontinuance in .357 Magnum makes total sense. S&W still makes 5 J-frame models in .357 Magnum, according to the website, so some folks must still be asking this nonsensical question.
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The longer cylinder required, never mind any longer barrels, totally ruins the compactness of a J-frame in .38 Special. It's pretty close to the ideal concealment handgun around in terms of size and weight and especially for those of us who do not expect to get into a gunfight requiring 17 rounds but, okay, I do carry a higher capacity 9mm instead of a J-frame when I think it's appropriate but, still, my 9mm Walther CCP is nearly the same size as my M 649 so concealment is just as easy. So I'll give a compact 9mm a nod there but, mostly, my M649-1 in .38 Special is my go to, pocket or belt carry, EDC.
The recoil of a .357 Magnum in a J-frame is brutal, I don't care who you are, and it is not worth the tradeoff.
Everything you need; nothing you don't:
As an aside, snubby K frames in .38 Special are pretty close to the same ideal. YMMV as always.