I thought this might interest people:

At General Girrfin's headquarters, I saw a shell (one of two or three) which had been fired at his lines during the day, from a sort of iron-clad car on the railroad, which at this point runs obliquely to the river, and for some distance is within easy range of the northern bank. Officers who saw the car at first supposed it to be a water tank, were were speedily undeceived. On nearing it belched forth a great volume of flame and smoke from the mouth of a 70 pounder rifled gun. The shell I saw measured six and a half inches in diameter, and weighted fifty seven pounds which, added to the weight of a piece of of copper, broken off one end, just about seventy pounds. Philadelphia Inquirer, June 11, 1864.

Bryce