S&W made an L-frame 44 magnum and it is holding up quite well with a steady diet of full magnum loads . I have no doubt the new 19's/66's will do the same with 357 magnum loads .
The down fall of any make of 357 , be it Smith , Ruger , Colt etc is the usage of light weight bullets , 125 gr or less . That is what eats up forcing cones if loaded with max charges of W296-H110 ( ball / spherical powders ) . Use the light weight bullets , but in a 38spl load . For the 357 , the lightest I would recommend is 140 gr . That long cylinder on the 19's / 66's is made ideally for the " Keith swc " , 173 gr ( Lyman 358429) . Seat that bullet on top of 7.0 grs of Unique , 7.5 WSF or 13.5 grs of Alliant 2400 and you have 2 perfect loads for midrange and 1 upper end load . You will wear out before the gun does . Regards, Paul