Miller, if I may offer what I have found in my readings and search for more depth concerning the .410 ............
I appears that the year was about 1882, in England. There exists a box of .410 shells that are believed to have been manufactured just after 1880. There are advertisements in 1882 issues of Shooting Times and The Field for the .410. Eley advertised a 2" Gastight loading in 1885. Sounds like that narrows it down to the very early 1880s.
As far as the "Continent" goes, there is mention of the .410 as early as 1886 in French cataloging. It is actually for a 12mm cartridge. Ronald Gabriel contends that, even though the 12mm cartridge is slightly larger than the .410, most consider it the European equivalent of the American and British .410.
There is much more info about the .410 in Gabriel's excellent book, IYI. And, Researcher may have more ........... I hope!
SRH
