I shot an adjustable sight assy loose on a 686 during a bowling pin match one time. That was after many thousands of rounds between my father and myself. S&W replaced it, but it was VERY loose. For the rest of the match, I had to hold low and line up the top of the gun with the pins.
Most S&W adjustable sights have that slight movement to them, as long as it's not effecting accuracy, it's normal. I've always felt that the S&W adjustable sight is a little fragile, so I'm planning to try C&S's fixed sight setup on one of my 629's.