I am actually very curious about this. If the sights are locked to the slide essentially, and the barrel is machined correctly, and locks up tight to the slide. why would slide movement matter that much. Assuming it isn't ridiculous and wobbly, or binds up cockeyed.

I shoot bullseye pistol with a Ruger Mark III, and that thing is very accurate because it is all solid. Same basic concept of the S&W 41. No slide, just a bolt back and forth. Never fully understood the slide/frame issue. I hope it gets explained.