I think here in the US large scale interest in the small bore goes back to when Remington introduced their model 17, ne Ithaca model 37 & Winchester offered the model 12 in 20 bore as did a number of other makers. It was perhaps the general prosperity after WW1 that made for a lot of interest in the smaller framed lighter field guns & repeaters had come of age & were both accepted & affordable by many. They just made good sense for upland game that didn't require much shot payload in order to bag the game being sought. Cartridge weight & bulk as mentioned earlier is also a real enough factor when one is going to be trudging about afield all day.
In a double, one has but to heft or carry any of the older Ithacas in their small bore iterations to understand what a delight afield they are .. a good set of barrels with minimal breech mass and just enough wood to let it be admired and pointed well.
Post WW2, Remington made inroads with their 1148 28's that mostly got pounded to death w/1oz. commercial loadings, but many a Texas bird hunter thought they had found nirvana w/that combination in the 50's & into the 60's. They were ultimately replaced by the 1100 lightweight's, still a modern favorite.
Beretta executed the O/U small bore to prefection in their ASEL 20's & Ithaca brought in the delightful SKB made model 100's w/25" bbls. for a while, which, IMHO, was perhaps the best modern made 20 double out there for overall fit, finish and features in a bargain bird gun!
Today, one has the majority of registered skeet shooters using 20's in the 12ga. events to improved scores and Remington even markets a 'managed recoil' 7/8oz. target load that should be about ideal for most small upland game.
If dove & quail & such are the quarry, a 20 is plenty & so is 25 grams of #7 shot.
OK, enough post turkey day ramble; off to shoot a couple of hundred sporty clays targets w/a heavy 12 and walk off some of yesterday's excesses. Best to all here! tw
