I am sure that a true Fosbery type paradox or explora/fauneta was a development of the breech loading shotgun.
However, I am wondering, if a soft cast ball or slug, sized to slip past such rifling (bore diameter) would obturate upon firing that the effect would be the same in a muzzle loading paradox.
Such a projectile, once passed the rifled choke, would simply fall down the bore and wouldn't stay pressed upon the powder charge very well.
Now, if one had a projectile that was sized to the groove of the choke (bore of the smooth portion of the barrel) and pressed past the rifled choke imparting the rifling onto the bullet, then I could see it working to some extent but there is no way to insure that the rifling imparted onto the bullet going down would in any way line up to the rifling on the way out.