mrlizzard,
It has been done, but with the rifling spinning the shot cup the centrifugal force outward blows the pattern to a donut shape. A 28ga shot cup fits nicely into the .50 caliber bore and can work for some VERY close shots like at sitting bunnies but not good enough to take a turkey cleanly at more than 5 feet or LESS.
***Disclaimer:*** I am not promoting this practice mentioned above, just merely stating that it has been done before and in no way should it be considered a safe practice and is not recommended by any manufacturer that I know of. I just know a couple knuckle heads that claim they have done this and my report is based on their report and nothing else, that's all. :wink: