You can fire a .45LC in a .410, but with no rifling it won’t be very accurate. A .410 in a .45LC can damage the rifling if I remember correctly..45/.410 pistols usually have maybe an inch of rifling, then the rest is smooth barrel. A complete smoothbore pistol would be illegal unless you pay the $200 NFA tax on it, so the inch of rifling is for legal reasons. I’ve always wanted to get some of those Leinad .45/.410 kits to built. They’re like $40 each or less in kit form! Then you just need to make the breech face and frame and weld it. A couple other neat .45/.410 pistols are the Thunder Five and the Bond Arms Derringer.