Bill's PC 4506 is a dandy, and if indeed one-of-a-kind (no reason to think it's not, by the way) it's a super score. What's interesting too about this pistol is its "PCZ" prefix -- which seems to be the one that the Performance Center used for a few different models that were very limited runs. I would have to go back and do some re-researching but I am sure I've seen this PCZ prefix on at least two other Performance Center guns.
Also interesting is that the PC actually marked the model number on the frame, above the serial number, the way the production side of the house does it. Sure does help make identifying the models a lot easier when the box isn't available to look at!
