Foster designed slugs are supposed to wobble and I doubt the .o4-.05" difference between a .410 bore and a .45 cal barrel would normally make much difference. Although, from what I can find on the 'net, the overall poor design of the .45-.410 concept can mess anything up. But then, looking at these firearms and their designs, they weren't intended to be accurate. At least not by any normal definitions of the word.

The excessive bore diameter is probably also what is causing the bad groups of 000 buck loads I've read about, since they are able to start spreading out of alignment inside the barrel. There were good reports about the Winchester PDX load with lead discs though, and it would stand to reason that lead cylinders instead of round balls would do better.