Timothy is absolutely correct, historically and factually. The Model 19 S&Ws most often were the victims, the Model 13, too. This was 'fixed' when S&W dropped the M19 and went to the L frame revolvers, I believe..... Shooting the heavier 158/160, 173, 180, and 200 gn slugs with slower burning powders does not cause the same flame cutting as did the faster burning powders used with the 125 gn slugs. The flame cutting is actually 'etching'. I have never seen a revolver that has undergone flame cutting or etching on the underside of the topstrap that has suffered any weakness or structural damage to that part of the frame or that has become unsafe.
The occasional use of the 125 gn self defense loads should not 'hurt' your revolver although I would opt for regular practice with either the 158 gn slug at magnum load levels or heavy 38 specials and then carry your defensive revolver with those self defense loads.
If you do not reload I would suggest you consider getting started or at least think about it. The tree-fiddy-seven is way too much fun and way to versatile not to reload for it; it is one of my favorite calibers. jmtcw.