For scratch removal on standard S&W satin finish stainless, use a "Scotchbrite" synthetic blending or polishing pad.
These are similar to the green synthetic pot scrubber pads sold in grocery stores.
Many hardware stores sell them in the sandpaper department, and you can buy them at automotive stores where they're sold for paint sanding.
These come in various "grits".
Simply rub the scratched areas until the scratches are either removed or blended in, then use finer grits until the original finish is matched.
Then "stroke" in the same direction as the original grained finish ran to finish blending the area back into the gun's original finish.
To finish off, you can use Mother's or any other good metal polish.
Just remember, the metal polish will give the gun a shinier finish than original, and you have to do the entire gun so as not to leave a "blotchy" look.
By using just the blending pads, you can match the original factory finish.