I would check with the Browning historian about your gun. US marketed three barrel sets used a different serial number series than normal twenty gauge guns. (Unfortunately, I have not been able to confirm the separate serial number theory. I will continue to look.) Your gun sounds like it is in the 20 gauge series (Schwing). If you can post a picture we would like to see it. Some three barrel sets were sold out of the UK and other countries. Who was the famous skeet shooter who owned your guns? If he goes back that far, I may recognize the name.
