In my experience black powder is more of a stabilization of a ball or slug with slow burning powder over a long barrel. Which when spinning gives it more accuracy in theory. Were with smokeless powder its a fast burn an the whip of the bullet down the barrel needs more control. If the barrel is attached to the wood stock it sorta throws off the accuracy. This is my own opinion. I have seen some accurate muzzle loaders shoot groups that center fire rifles only can dream of.