History of the 2-bore rifle is somewhat enigmatic. Certainly there were a number of large bore-caliber punt guns produced in the mid nineteenth century for use in waterfowling. There is even record of adaptation of quasi two bore rifles for hunting elephant and other large game in 19th century Africa. These rifles were mostly smoothbore muzzle loaders of varied bore diameter and none are known to have possessed a true 1.325″+ bore or groove.
Bore caliber rifles utilizing modern fixed ammunition were eventually produced in limited numbers and did find their way to various hunting grounds. These seem to have peaked in size at 4-bore and a generally recognized standard of slightly less than the official 1.052″. A few 2-bore rifles have been produced in effect by lengthening existing 4-bore cases and increasing projectile weight to 3500 grains with corresponding charge weight.
There are serious engineering difficulties which make the application of a true 2-bore sporting rifle a difficult prospect. Recoil, weight, utility, and cost put significant constraints on the designer. After considerable effort, S&H believe they have satisfactorily addressed these issues with a complimentary rifle and cartridge pairing and the use of some innovative technology.
Shooting Times UK fired the 2 bore at the West London Shooting School back in May 2008.
Vince Lewis has a lot more information about the 2 Bore on his site: http://www.vincelewis.net/2bore.html