Just to add to the breadth of this conversation, I have a 3.67-inch bolt of the same pattern as Carl's, which came out of one of the northern Virginia battlefields. It had been fired and hit something hard tasking a chunk out of the nose.
As to the use of the iron Schenkl fuses, I found parts of one on the Antietam battlefield, down by Burnside's Bridge. Since the only rifled shell fragments I found were from 3.4-inch Schenkls fired by the Union Naval Battery there, I assumed those were the shells they came from.