Their principle value comes from being able to lob shells behind an obstacle such as a fort or a hill. Unlike modern mortars, those used during the Civil War were bulky devises and mounted at a fixed angle usually between 45 and 50 degrees. They were not very accurate and depended solely upon the amount of propelling powder to determine their point of impact. .
Shells, hollow ammunition filled with gunpowder and equipped with a fuse, were the most common type of explosive artillery round used during the Civil War. Fuses could be either timed so the round would explode after a certain number of seconds had elapsed, or were percussion so the ammunition would explode upon striking an object. Shells were generally used as long range rounds, meant to explode among an advancing enemy or used to blow apart enemy forts. .
Solid shot was a kinetic energy round. Its speed and mass were used to penetrate walls, fort and armor. To produce any type of casualty effect, the round would have to actually strike the target. Solid shot was particularly used against ironclad ships where a shell would do little or no damage. During one test an 8 inch Brooke rifle with 16 pounds of powder fired a 140 pound ball 260 yards and penetrated eight inches of iron backed by 18 inches of solid wood. .
While there are many accounts of troops charging bravely into a "hail of grape" there is little fact in this. Grape shot was used very little on the land battlefield during the Civil War. The ammunition encountered by the soldiers was called canister, one of the war's most deadliest rounds. Canister was basically a tin packed with sawdust and musket balls which, when fired, spread out and turned the artillery piece into a giant shotgun. At close range against masses infantry this round was devastating, cutting huge swaths through the attacking men. .
Grape shot was widely used in the 19th century wars, but by the time of the American Civil War, grape was primarily used by navel gun crews.