Not all 9 major loads are created equal, with a slow powder like 3n38 and a barrel with no holes you can actually make major with a 9x21 book load. The faster the powder the further outside the book loads you have to go; holes in the barrel and/or short barrels take more powder.
Its actually safer than you might think, I've found when you push a slow powder too hard it just stops gaining velocity. I'd bet there had been more blown up guns with 40 major, super fast powders and heavy bullets. With something like 3n38 you cab fill the case to the brim, jam a bullet down and shoot it without issue.