A paradox-style straight rifled section at the muzzle, should have a slight choking effect on a shot charge, as in effect, it is a rifled choke. How well it would work when muzzle loaded,
is the question. If using Track's felt wads, it might just work quite well, tightening patters, that is. With solid shot (ball), it's hard to say.
Knuckle balls in baseball, usually gave up and down (vertical) oscillations, making the ball difficult to hit. At supersonic speeds, it's difficult to say what would happen as speed changes
"things". We do know that the higher the speed, the longer the distance a smoothbore maintains accuracy.