The 28-gauge 1 ounce load was loaded in the US, at least for a while, a number of years ago. Jack O'Connor writes in the Shotgun Book.

In the late 1950's, Federal Cartridge Company kicked over the traces and loaded a 28-gauge magnum shell with 1 ounce of shot. The other companies followed suit.

I expect that the 28-gauge "magnum" was 3-inch.