I have one of the early Model 627-2 Performance Center revolvers. The retaining pin for the frame mounted firing pin is vertical and is held in place by the underside of the rear sight. I remember reading that there was a problem with some mounts allowing the retaining pin to fall out and disabling the gun. This was a long time ago, and all may have been modified by now. Anyone have a mount they recommend? Inexpensive is better.