The typical 2 1/2" British game gun, until 1954 when the rules of proof changed, was marked for a 1 1/8 oz shot charge. When using Brit game guns for wild American ringnecks over dogs, I usually shoot British 1 1/16 oz loads (Kent Gamebore Pure Gold; previously Eley when they were more readily available). However, I also worked up a reload of 1 1/8 oz at about 1200 fps, pressure around 7,000 psi, that I'd use in my tight barrel. I did not shoot a steady diet of those, but I didn't find recoil to be an issue in 6 1/4# guns. Of course you're not shooting a lot either when the limit is 3 birds a day.
While the British pheasant harvest likely wouldn't approach American numbers--especially going back to the years when we were regularly killing from 2 to 2 1/2 million birds annually in just two states (SD and IA)--it's undoubtedly true that some shooters in the UK rack up annual totals that no American is going to approach. One of my regular fellow "guns" in Scotland shoots 50-60 driven days a year. I don't know that he keeps track, but that's easily going to run over 1,000 birds a year.
As far as distance is concerned: those who participate in those shoots offering truly tall birds (note: these are NOT the norm in British shooting, by any stretch) almost certainly kill more long-range birds than anyone shooting pheasants in this country.
All of that being said, it's apples and oranges. Driven birds are mostly shot as incomers or crossers, with their vitals significantly more exposed than they are when we put them up over dogs. An ounce to 1 1/16 oz of Brit 6's (slightly larger than our 7's) through something around a quarter choke (.010) is quite effective on TYPICAL driven birds, where a 40 yard shot is really long. Those seeking out the tall birds use guns more like what we see in the hands of sporting clays shooters: heavier and with longer barrels. And throwing heavier loads of larger shot. There were good articles by Chris Batha and Vic Venters on these "high bird" guns and loads in a recent issue of Shooting Sportsman.
