During the American Civil War, much of the outcome was decided by the use of cannons. Most of this artillery was used in concert with large field armies. These cannons, called field artillery, were generally used in accord with their specific size and purpose.
The 1860s were a time of major industrial development and innovation, and therefore there were many different types of cannon used in the American Civil War. Most, however, can be placed into one of three categories: smoothbore barrels, rifled barrels and howitzers.
1857 Napoleon Cannon pictured above.
Manufacturers made smoothbores in greater numbers than any other cannon in the Civil War. Because of the cannon's low cost and ease of manufacture, the Confederate armies made almost exclusive use of these types of cannon. The most common variation was the 12-Pound "Napoleon" (see plans)," so called because its usual ordinance, a solid lead ball, weighed about 12 pounds. It was made from solid bronze, had a 4.62-inch bore, was 66 inches long, weighed 1,227 pounds, and had a maximum range of 1,619 feet at velocity of 1,440 feet per second. Because of its smooth bore, the weapon was not very accurate, yet its ability to fire a cannister (a cylinder full of many small projectiles) made this cannon very effective at short range, much like a large sawed-off shotgun.
Because of the need for precision and high-quality metal, rifled cannons were more expensive to produce. Federal armies had more rifled cannons than did the Confederates. Among these cannons, the most heavily produced was the 3-inch Ordnance Rifle, so called because of its 3-inch bore. Made from wrought iron, it was 69 inches long, weighed 820 pounds, and had a normative range of 1,830 yards. Because of its rifled bore, this weapon had a greater range and was far more accurate than its smoothbored counterpart.
Howitzers were characterized by their high trajectory designed to lob their projectile over the top of enemy fortifications and/or the trenches from which they were fired. Like the Napoleon, a common 24-pound howitzer was smoothbored, and made from bronze. Two popular versions of the howitzer were the Prairie Howitzer and the slightly smaller Mountain Howitzer. The 4.62 caliber brass Mountain Howitzer was a 53 in long cannon on a carriage capable of being disassembled and carried by pack horses.(View 12 Pdr. Mountain Howitzer on Second Model Prairie Carriage plans and 12 Pdr. Mountain Howitzer on a Pack Carriage plans.) It had a 5.82-inch bore, was 64-inches long, weighed 1,318 pounds, and could fire a solid lead projectile weighing about 18.4 pounds at a range of 1,322 yards at velocity of 1,060 feet per second. Because of their heavy weight, howitzers were usually the last form of artillery to arrive on a battlefield in both Confederate and Federal armies.
Excerpts taken from: http://www.ehow.com/info_8079544_civil-war-cannon-specifications.html