The now discontinued 327 4" scandium frame, I don't think there is a lighter 4" .357 than that.
John
Second thought the lighter the gun the recoil is increased. The weigh we save we increase on the other end. I understand the weight savings but do you plan on getting a light 357 and shoot 38 specials out of it?
I think that would be the Model 520. It was the same configuration as the 620 (ejector shroud, 4", L-Frame), only with a scandium cylinder.
There are two different S&W model 520's. The NYSP N frame gun, and the L frame gun I mentioned above.
Wasn't there a light night guard model?