Thank you WVsig for your time and sharing your knowledge. You've been a great help, this has been a really enjoyable research project. Also, thank you one and all for your contributions. The stamp mark within the the side is indeed a full diamond shape surrounding the number 5 hence dating the slide year 1975. The chrome barrel exterior and bore is pristine. Yet I can tell someone has grinded and polished the feed ramp; perhaps this would indicate it once had had the older hump feed ramp design that was best suited for round nose bullets. It's a two piece barrel. Your right WVsig, theres no proof marks, just stamp marks. From what I've gathered FN added the hognose bushing at some point during the "C" series and then dropped the "C" from the serial number system and changed to a darker bluing by the 1970's. Thus it looks like they pulled a 1975 slide off the self (and perhaps other 1970's parts) stamped it with a 1984 serial number letter code and shipped it out for North American distribution during the year 1984. My dealer found it at an estate sale.