Just doing a quick review of the article, looks like Bell tested about 15 different loads, including a couple each 3" shells and round ball rifle loads.
Something we've failed to mention here is that you can get yourself into trouble if you're shooting an older gun--almost always 19th century I think--that has a forcing cone that's more like a "step" than a taper. Charles Fergus reported on that in an article he did for Shooting Sportsman. He was getting a loud report and blown ends on British 67MM shells which, according to the information on the box, are approved for 2 1/2" guns. Those same shells worked fine in a 1930's vintage 2 1/2" British double. But he had to use true 65MM/2 1/2" shells in that older gun with the "step" style forcing cones to avoid problems. In those guns, it's pretty obvious that you would not want to use reloaded 2 3/4" hulls.
