Post - BP factory .38 S&W loads have always been loaded with light charges of smokeless powder which approximate the chamber pressure characteristics of BP loads and are safe to use in the older BP revolvers. In fact, factory smokeless loads have been safely used in the old revolvers for over 100 years.

Of course "Hot" smokeless powder loads can be made up by reloaders which could cause damage, but that's not what the factories sell. In a suitable modern revolver chambered in .38 S&W, the cartridge could easily be loaded to .38 Special performance levels, but of course those should never be used in the old top-break revolvers.

Some people believe there is some unusual and destructive "pressure spike" associated with smokeless powder which does not occur in BP loads. There is no evidence of that.