Maybe I'm behind the times but I don't follow those that buy a Sharp's or Pedersoli Rolling Block of a given caliber to fire smokeless powder in it. Why? these rifles and most calibers were originally meant for black powder. I have a 45-70, had a 40-70SS and a 38-55. They never saw the first dose of 4759, Trail Boss, 2400 or any other smokeless powder. To me that just takes away the fun of it all. You may as well just buy a 30-06 and load it with H4895.
For sure none ever had a J-bullet through them and never will.