https://www.youtube.com/watch?v=33-RnJekpLU
Something going on here worth looking into. This would indicate aerodynamics being a major factor in shotgun slug accuracy. Interesting to note that spinning the pellet actually destabilizes the pellet but then that was with a rifled choke, not a rifled bore.
I am of course very interested in casting for and firing slugs out of my single barrel break action. Mine is a long barreled choke gun that I only once used for pest birds. I also have a 410 that I got specifically for firing slugs. So this video has given me hope and ideas.