Mine was a shotgun, barrels shortened to 24".
The 7 dram black powder loads and the smokelessSR4756 loads in my gun gave me 1,550fps with a 480gr. RB. (undersized in a cup-wad) The wad columns of course, were quite different, but both used the cup wad for centering the ball in the bores.

I tried the same system in my rifled Mossberg 835 tube and they were quite accurate in my limited testing at 25 yards - single 1 1/2" hole for 5 shots offhand. but then, a good load in a smoothore will do that too. 25yards is too close for testing accuracy.