The dual spring setup requires a smaller dia rod. When S&W repaired single spring units they would use the smaller rod and put a bushing in the slide to fit it. They don't supply the single spring anymore, you would have to get one from Wolff(who doesn't make the dual spring, go figure?). I never had one so modified, but I take it the bushing is pressed in like the muzzle bushing so that the smaller rod doesn't move around. I would call S&W and see if they will modify your gun under warranty.