Franc, Doverham, checking the Blackbern site as well. Was thinking of patched round balls and drams of black powder, as well as working up smokeless loads with something like Brennekes. I think that to get a Fosbury-style "cotton-spool" slug to be accurate, I would need rifled choke tubes for the paradox effect. Agree it would be pure serendipity to get an unchoked smoothbore double to spit slugs into the same space.