Leadslinger...No, No, you post is right on the button! The old smiths at S&W said the secret was what abrasive that was used...To coarse ane one gets Wear! The idea was to just burnish and smooth the action, not remove metal. I have one S&W 686-3 that was hand lapped by one of the old masters that had retired from S&W. Another interesting thing I was told is that stainless firearms are much harder to smooth up than blue steel. It had something to do with the makeup of the steel. It is true that the older firearms where works of art, however the new offerings are much stronger!There is a newer method of polishing that is being installed. The parts are secured to a frame, immersed in water that is full of cone shaped rubber things about the size of your thumb with abrasive in them, sound waves shot through the water. The method does not round off the corners at all. There can be a hundred or so rifle actions or about three hundred pistol actions done at the time. I saw it demostrated some time back. It may well be the answer for the future.
Best Regards, James