Building a Williams Gun
The story is here. The Williams Gun was a Confederate creation. It was a rapid firing, carriage mounted, rifled gun of 1.5" bore. Its projectiles were gigantic Minie type ones, cast in lead, and explosive ones were made with a cavity for black powder and a nipple for percussion cap on the nose. (Safety was not a big concern in Civil War artillery). Its main purpose was long-range sniping at artillery limbers and caissons -- the explosive rounds would have done a good job of detonating those.
I found a record of one scoring a hit, in the surgical volume of the Official Records of the War of Rebellion. A sketch depicted a projectile that hit an officer's horse at the Seven Day's Battle -- it was a Minie type, 1.5" diameter, with a big cavity in the nose. The authors speculated that it might have come from a gigantic sniping rifle of unknown type. My guess is that the gun was being used for sniping at people, and so the crew omitted the explosive charge.