Billy Dixon indeed! Pish posh! he was using one of those old fashion black powder guns. With a modern smokeless load in a fancy shotgun a guy could do way better. Right!?! This guy obviously is. He wouldn't stretch the truth a bit would he? Yeah, likely more like 4'.
But as BB says "...anything is possible". Just because I can't do it doesn't mean it can't be done.
Gp are you using pure (or very soft) lead for your Lee slugs? So far I've only used range scrap. Both Lee and Lyman recommend soft lead. That probably allows both slugging up to match the bore and "reforming" some to match wad petals.
Megasupermagnum you don't happen to have any of those old Buckbusters around do you? I have read about those and I believe I have a reloading article from when they first came out. I'd like to know diameter. As I said, I believe the Lee slugs have too much taper to them and would be better if they tapered at the rate of typical birdshot wad petals which is something like 0.003" over the length. If the slug tape matched that the wad petals should be compressed nice and even like which I think has to be a good thing. Then I'd be expecting 4" groups at 250 yards for sure!
Longbow