Fort McHenry 10

During the American Civil War it was discovered that rifled artillery was not only more accurate than the smoothbore type, but also had greater penetration. The stone or brick masonry fort was rendered obsolete almost overnight. Cannonballs bounced off ironclad warships.
Both sides in the war manufactured and purchased the latest rifled artillery but they already had on hand thousands of smoothbore weapons. An industry rose up to convert smoothbores to rifles by boring them out, inserting rifled sleeves and re-enforcing the breeches to handle the increasd pressures.
This Rodman cannon, originally a 10" smoothbore, has been sleeved to 8". Instead of an iron ball, it will now fire cylindro-conoidal projectiles of various designs and weights, some solid and others filled with explosives.