A shot tower is a tower designed for the production of shot balls by freefall of molten lead. The shot is used for projectiles in firearms. In a shot tower, lead is heated until molten, then dropped through a copper sieve high in the tower. The liquid lead forms tiny spherical balls by surface tension, solidifying as it falls. The partially cooled balls are caught at the floor of the tower in a water-filled basin. The now fully cooled balls are checked for roundness and sorted by size; those that are "out of round" are remelted. A slightly inclined table is used for checking roundness. To make larger shot sizes, a copper sieve with larger holes is used. However, the maximum size is limited by the height of the tower, because larger shot sizes must fall farther to cool. A polishing with a slight amount of graphite is necessary for lubrication and to prevent oxidation.