From 1891 to 1899, Union Metallic Cartridge Co. only offered loaded shells in 10- to 20-gauge. They offered both brass and paper NPEs for 8- and 4- gauge. By 1900 they were offering loaded 8-gauge shells.
In their 1900 catalog Union Metallic Cartridge Co. offered quite a range of 8-gauge loads, bulk smokeless matching the black powder loads.
8-gauge TRAP Shells 1900.png
They must have discovered some of those loads in smokeless were too hot and cut the smokeless loads back by 1901 --
8-gauge TRAP Shells 1901.png
1903 --
1903 UMC 8-gauge Loads.jpeg
1905 --
8-Gauge Trap Shells 1905.png
Threaded Mode