Rifling
In 1849, a French army officer, Claude-Étienne Minié, invented a bullet with a hollow base named for him called the Minié ball. When fired, the bullet expanded to fit the rifling inside the gun barrel. This gave it even greater accuracy over a longer distance. The British used it in the Crimean War against Russian forces with tremendous success. At the time of the American Civil War, both the Union and the Confederate armies were using smoothbore muskets out of necessity. But soon rifled muskets using the Minié ball replaced the smoothbore muskets. The effects were to devastate the opposing army at much longer distances.