The Model 1841 cannon was a lightweight gun used extensively during the Mexican War. Though fairly mobile at 900 pounds, its softball-sized shot was too small to do much damage. It was easily outranged, especially once rifled guns came into use.
An extensive number of these 6-pounders existed at the outbreak of the Civil War, and were pressed into service by both sides. When the advantages of rifled guns that fired elongated projectiles across greater distances became apparent, the government began to convert older smoothbores into rifled weapons.
A common artillery piece that was converted was the Model 1841. Accuracy and range were greatly improved by re-boring its 3.67” caliber to 3.8” and rifling it in the "James" fashion to accept the patent projectiles designed by General Charles T. James. Hence, it became a James rifle.