Having watched quite a bit of video of game bird shooting in the UK I was very surprised that the O/U seems to have taken over as the gun of choice now. Despite the tweeds and ties, 'proper' gumboots and all the other associated stiff upper lip bits that go with UK hunting, even the top guns have gone to the dark side with the O/U gun.
While I did say dark side, this in jest and they, like me many decades ago, have seen the light and recognise the O/U as being the leader in the field for both competition and sporting use.