If you were in Europe, smith revolver, you could tell them you have a lever-action 12mm!
The .410 shotshell was first made in Europe, where it was designated, "12mm."
Pinning down the exact year or country of its origin is difficult, but it was listed in Geman catalogs as early as 1910.
In the U.S., it was first produced by Remington Arms - UMC and offered in 2" and 2-1/2" lengths, in both shot and single ball loadings.
Early Remington ammunition may have both .410 and 12mm designation on the head, because it was intended for export to Europe and other continents, as well as for use by U.S. shooters.
Such ammo would be a good collectible today; don't shoot it.
Winchester began producing .410 ammunition in 1916.
About 1934, Winchester brought out the 3" .410 shotshell, for use in its pump-action Model 42. This shell, with its 3/4 ounce payload of shot, rivaled the 28 gauge and has all but replaced it.
I have a Marlin Model 410 lever-action shotgun made about 1929. It was only made until 1932. My shotgun is in fine shape and bears a serial number of U5XX. I have no idea what the U prefix means.
It's a wonderful little shotgun, built on the Model 1893 frame, and handles well. It will only take 2-1/2" shells as the action is to short to handle 3" shells.
The only downside to this shotgun is the bulbous forend on it. God knows why Marlin chose such a huge forend. The claim is that it made sighting easier but I've found it a distraction.
Nonetheless, some years ago I bagged two blue grouse in rapid succession with it, in the Blue Mountains of southeastern Washington.
The .410 is a good cartridge but for most purposes the 20 gauge is better. I later chose a Remington 870 Youth Model in 20 gauge as my grouse and thick woods gun.
It's wonderful: short, short barreled, light and comes to the shoulder naturally.
And now, you probably know far more about the .410 than you ever wanted to know!