I'm another who says I'd stick with the 642. Snub revolvers are close range, minute-of-miscreant defensive guns. For that, I think a good .38 Special +P load is effective and much easier to control for a second shot than a light .357 Magnum. You're already becoming proficient with the 642. Shooting .357 stuff would add more factors to consider.

But then I'm not a fan of Airweights, Airlights or Gnatweights. I like steel for its heft, recoil damping and durability. If you're set on a .357 snubby, the 640-1 would give you the option of what an awful lot of people do: carry it loaded with +P .38 Special, with the choice of .357 if you feel the need.

You know what they say about opinions, but that's mine.

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Oh well, what the hell.