Some great input here - thank you. I use fibre wads for virtually all of my shooting so less of a concern there.

As regards Teague or Briley choking, I may well be mistaken here, but have always been wary of these options as I thought they required some significant lapping out of barrel thickness to accommodate them and/or the incorporation of screw threads in the end of the barrel?? Not something I am keen on doing to a lovely set of old Damascus barrels, especially on a waterfowling gun?