The following is from"Wikipedia" so take it for what its worth. This does as I recall though reflect info from the site I mentioned finding some time back. I have no idea now as to how I accessed it, but it did appear to be well documented & that the True .410 bore preceded the .44Xl etc.
Origin
Lancaster's pattern centerfire and pinfire .410 shot cartridges first appeared in Eley Brothers Ltd. flysheets in 1857. By 1874, Eleys were advertising modern centerfire .410 cartridges.[1] It appears to have become popular around 1900, although it was recommended as "suited to the requirements of naturalists, and for such weapons as walking-stick guns", presumably for self-defense, in 1892 by W. W. Greener.[2] The first ammunition was 2.0 inches (50.8 mm) long, compared with the modern 2.5 and 3.0-inch (76 mm) sizes.
