Larry, some folks MIGHT be willing to let a London built pigeon gun travel in the duck boat. But, I don't know any of them. What you are describing is a fairly rare and very expensive gun, in any event. Those tungsten loads are way, way up there on pressure as well. Just because an old, expensive, London fowler was proofed at that level, 75 years past, are we to be comfortable subjecting it, on a regular basis, to that level of pressure today?
Ted
Ted, you probably need to check prices on those Repro Steel Shot Specials. They ain't exactly Stevens 311's. Anyone that would be willing to take a Repro on a duck hunt would probably be willing to take a Brit double.
As for the TM pressure issue . . . yes, that would indeed be a problem, IF one were to shoot the Kent loads made for the American market. However, right in front of me I'm looking at a box of Kent "Impact" TM loads. 2 1/2" shells, "fibre" wads (those darned Brits can't spell!), #5 shot--which splashed whole bunches of ducks back in the lead shot days. And the box further confirms that they are suitable for use in guns with a 3 ton or 850 bar proof. I have shot them on pheasants in my 2 1/2" Brit guns, on those rare occasions when I venture into areas requiring nontox for ringnecks.
Too bad they've gotten so darned expensive. But then so has lead. Pretty soon the steel Nazis may convert us all not because steel is better, but because it's cheaper!