The smallest civil war bronze smoothbore howitzers had 3.65" bore and fired a 6-pound round ball. The largest howitzer had a 6.40" bore and fired a 32-pound round ball.
The smallest civil war steel rifled cannon was the 12-pound Whitworth with a 2.15" rifled bore and the largest was a bronze 24-pound James with a 4.62" bore. The rifled cannons fired explosive eliptical shells rather than a solid or explosive round ball. The eliptical shell accounts for the heavier projectiles with a larger powder load compared to smoothbore cannons that fired a lighter round ball of the same bore size.