"Bolt" in ACW parlance is I believe used for any rifled solid shot. Bolts could be armour piercing, but such characteristics were primarily for very short ranges and very flat trajectories. (It wouldn't take much drop in velocity to seriously reduce penetration of plate, and anything off perpendicular also was likely to deflect.)

Smoothbore solid shot by its nature was proportionately heavier than case or shell. This greater density somewhat improved its accuracy and its range at the same firing angle. I'm not sure if this applied to rifled bolts to the same degree since the windage effect on efficiency was absent for the rifled round...so I suspect the ratio of initial velocity of shot to shell may have been lower for rifles than smoothbores. (Smoothbore shell propellant charges were also less than for smoothbore shot and this complicates comparisons as well. Initially, some of the difference in charges was to prevent larger charges from fracturing shells within the gun.)

Solid shot and bolts were able to more deeply penetrate masonry or earth, although shell could displace considerble quantities of dirt.

Smoothbore shell propellant charges were also reduced.

Have you been able to find a patent in Butler's name?