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Stone projectiles were simply rocks that had to be rounded-off so that they would not lodge in the barrel of the gun. Since spheres are actually fairly difficult to make, this required a skilled stone carver to make each piece of ammunition. Stone projectiles were the most common because stone is cheap and plentiful. In a long siege, armies could take stone cutters on the campaign with them and make more ammunition on location. Not all shot was spherical, however, and several antipersonnel-types include cubic and jagged shapes.