If you are dead set on using metallic brass hulls for the .410, there are a few minor issues...
444 Marlin will work fairly well, but it's a bit undersized, a bit shorter than a 2.5" shells, and the rim may be too small to eject reliably from most guns. .303 British brass must have the rims turned down and the neck blown out- never tried .303 brass myself.
I'd suggest getting the Magtech large pistol primed brass for the .410 if that is what you want (about $25 a box) and order the fiber, card and overshot wads for them. I'd have to look, as I can't remember the correct shellholder for them.
It is a lot less trouble to buy a brand new Mec 600 Jr. (avoid the overpriced used ones from fleabay), use plastic hulls, wads and powder than to fiddle with the brass hulls of any kind unless you just want them or just shoot blackpowder as plastic hulls and blackpowder don't work well for long together.