If you COULD find a 686 (L frame, not K) in a snubbie bbl, I think it would be a fabulous gun. I think that the "concealability" of any gun is almost completely dependent on it's grips, rather than the rest of the gun. ie, an 8 3/8 inch revolver would really hide just as easily as a 2 inch revolver. You've just got more bbl tucked down into your pants. It's the grips that are showing. And to further that, I believe that the "sharpness" vs "smoothness" of the grips are what makes one gun print more than another. Those bob handled 1911s conceal better than a regular square handled model because of the round off. Put smooth, rounded grips on a 686 and it will hide nearly as well as a J frame.
Width of guns is really not that different. Example -
S&W Chief's Special J Frame Snubby - 1 1/4" at widest
S&W Mod 66 357 Mag K frame 4" - 1 7/16" at widest
The bigger, six shot magnum is only 3/16 wider than the smaller 5 shot 38.
Height of the guns are also not that different. The magnum is 1/2" "taller" than the snubbie. 3 1/2 vs 3 inches, top strap to bottom of trigger guard.
Generally a 357 should be a stronger gun than a 38. And, of course, you can shoot 38s in a 357.
Carrying a 357, loaded with 38s, is a concept worth considering, IMO. In an urban situation, that magnum may go through the bad guy, then into the lady with the baby stroller 4 aisles over in the grocery store. Or through the burglar, your sheetrock, your horse trailer then into the paper boy out front.
In my case, if carrying a magnum, it's loaded with 38s if urban, hot magnums if hiking in the desert. One is protecting against overpenetration, the other is protecting against wildcats, bears and heavily armed drug runners.
Sgt Lumpy - n0eq