I am thinking it would need to be a sabboted slug if it were smaller with a sabbot it might just work.. Though I never looked into casting slugs. I have an old Mosberg .410 that was a birthday gift from my dad when I was 9 (27 years ago
) I still shoot clays with it. I have put slugs out of it. I still have a couple of boxes of them.
With popularity of the revolvers like the Judge, and Governor I would think that someone somewhere is casting .410 slugs. I saw one load that guy was shooting that was like a swagged wadcutter. They shot well out of a public defender.
Note I cast for a .41 Magnum. My Lee 210 grain Tumble Lube SWC mold drops at about .411 with standard wheel weight alloy.