Does anyone here know if the firing pin on a pre model 17 (1956) four screw and the model 17-3 or a model 17-4 firing pins are the same? I need a firing pin for a four screw S&W K frame .22 (1956 serial number) and can't seem to find one. If a 17-3 or 17-4 are the same it will make locating one a lot easier. Thanks for helping. BCM