I don't know if you have a 45-70 and a 410 crtridge available to compare, but if you look at the closely you will notice that the 410 rim is only slightly, if at all, larger than the case body of the 45-70. It might actually fall down into the chamber, but even if it didn't it would rattle around and would not be supported. Another thing that bothers me about the idea is the issue of shot in the rifling. Don't know what affects it would have but is it worth the risk? Not sure why you would even want to attempt such a thing in the first place.