Common Weapons
The system of ordnance adopted by the U.S. Army in the 1840's was the picture of simplicity: six- and 12-pounder field guns, 12-, 24-, and 32-pounder field howitzers, 18- and 24-pounder siege and garrison guns, and 32- and 42-pounder sea-coast guns. To this were added columbiads and mortars. The principal modification to this system prior to the War was the substitution of the light 12-pounder as the field weapon of choice. However, this system was soon made obsolete by necessity and technology.
The Civil War required a sudden and massive mobilization of military resources. The immediate need for field artillery resulted in the use of a bewildering variety of pieces, ranging from superseded ordnance to modern experimental models imported from Great Britain. Amongst the array of Armstrongs, Blakelys, Wiards, and Whitworths, it is still possible to identify a relatively small number of makes and models of muzzle-loading cannon that served as the workhorses of the Civil War battlefield....
....Attempts to convert some of these guns to rifles, using the James system of rifling, had only marginal success. Some have also been converted to "false Napoleons" by the National Park Service, grinding off the moldings and the sharp discontinuity between the reinforce and the chase, and enlarging the last few inches of the bore. The result can be quite confusing for the battlefield tourist.
http://www.cwartillery.org/aguns.html
