One issue you will find when trying to polish a Stainless S&W with a brushed finish is that the polishing will "highlight" the deeper scratches caused by that brushed finish.

The only way to get a truly "liquid" polish is to first wet sand the gun with 800 grit, then 1500 grit, and finally 2000 grit sandpapers. Then you will find that it will take on a superb finish fairly quickly with a good quality polishing compound applied by hand.

However, you'll also find that he barrel rib and cylinder cuts on some guns are pretty uneven, which means another cycle of sanding to get it even. In those areas it's best to use a block of soft pine and a backing for hte sanding strip so that you cut the high areas down and blend them in.

Finally, if your going for an extreme finish the final polishing must be done with all strokes in the same direction. No matter what polish you use, it will leave micro scratches that will catch the light from dertain directions. By making sure these micro scratches are all in alignment you can minimize those microscratches becoming visible because the gun has to be held "'just right" in order to see them.

PS, one of my jobs at work is building headers for custom show cars made from 304 stainless. For a "Riddler" quality polish, the polishing alone costs 800 dollars and involves about 50 hours of work.