Given how tightly most S&W sideplates are fitted, it's pretty near impossible to pry off a sideplate without at least peening the edges of the seam.
That's one of the first things I look for when I buy a used S&W revolver. It tells me whether someone's been inside or not, and by the severity of the peening, how often, how ham handed they were, and what I might expect in the way of "modifications and improvements." cough cough...
My .32 Long Regulation Police, made just prior to WW I, has a seam that is so tightly fit that it is nearly invisible. I was probably the first person to ever take it apart, and it was a gold plated SOB because it was literally welded into place.
I shudder to think what might have happened to the sideplate and that beautiful fit seam had I just stuck a screwdriver under the back edge of the plate at the grip and pried away.
As others have said, a rubber mallet's not the best choice for removing the side plate. I like to use a piece of softwood, like pine, to strike across the grip flats. If that doesn't work, I'll go to a nylon headed hammer.
If that doesn't work I'll use the 3 wood wedges technique described by Kuhnhausen in his book.
I've only had to resort to that once, on a pre-Victory model .380/200 a friend bought.
