(if not scratched to the copper substrate) is actually pretty resillient to most environmental demons
S&W NEVER, NEVER, NEVER, used a copper plating under Nickel! And the proper term is
Under-Strike. S&W Nickel is what is referred to as
Hard Plated This means simply that the plating metal is applied directly over the base metal, not that the plating itself is hard!
Colt tried using a copper under-strike for a year or two in the 1970s and had extensive finish problems with peeling because of it. At the time plating was being done by a sub-contractor. They had to re-finish many guns from that period. The plating operation was moved back to the factory after this.
If anyone ever sees a Nickel S&W that can be verified to have a copper under-strike that gun has been plated outside the factory, probably by a bumper shop! Plating of quality firearms is always hard-plating, only cheap, usually foreign guns will ever be seen with either a copper under-strike or so-called "triple plating", copper then Nickel and then chrome. That is how purely decorative chrome plating is applied.
No matter how many hundreds of times you see a reference to a S&W plated with a copper under-strike it is still wrong and the speaker/poster is simply parroting incorrect information he has seen/heard, just as you have! The often heard story that the copper is needed as a "primer" so the Nickel will adhere is simply a lie.