In the 1840s and 1850s, many smoothbore muskets had their barrels replaced with similar barrels that were rifled so that they could fire the new bullet. These "rifled muskets" or "rifle muskets" were long enough to serve the function of muskets in close formations of line and square, were as quick to load as the old muskets and as easy to use with minimal training. Yet the Minié-type rifled muskets were much more accurate than smoothbore muskets. Tests of a rifled musket firing Minié ball, and a smoothbore musket firing round ball, at various ranges against a 10 by 10 inches (25 cm × 25 cm) target, showed much higher accuracy for the rifled musket. From a smooth-bore musket, from 42% to 48% of bullets hit the target at a distance of 200 yards. At a distance of 300 yards, 18% of the bullets hit the target. For a rifle, the results were much better. From a rifle, 46% to 58% of bullets hit the target at a distance of 300 yards; 24% to 42% at 500 yards. This potential accuracy, however, required skills only acquired through advanced training and practice; a rifle-musket in the hands of a raw recruit would not have performed very much better than a smoothbore. Nevertheless, the musket was still a formidable force on the battlefield. At the beginning of the American Civil War, some infantry regiments chose to keep smooth-bore muskets, preferring them because they could shoot "ball and buck".