A shot tower is a tower designed for the production of small-diameter shot balls by free fall of molten lead, which is then caught in a water basin. The shot is primarily used for projectiles in shotguns, and also for ballast, radiation shielding, and other applications in which small lead balls are useful.
The process was invented by William Watts of Bristol, England, and patented in 1782. The same year, Watts extended his house in The maximum size is limited by the height of the tower, because larger shot sizes must fall farther to solidify. A shot tower with a 40-meter drop can produce up to #6 shot (nominally 2.4mm in diameter) while an 80-meter drop can produce #2 shot (nominally 3.8mm in diameter). Polishing with a small amount of graphite is necessary for lubrication and to prevent oxidation.
The process was invented by William Watts of Bristol, England, and patented in 1782. The same year, Watts extended his house in Redcliffe to build the first shot tower. Use of shot towers replaced earlier techniques of casting shot in moulds, which was expensive, or of dripping molten lead into water barrels, which produced insufficiently spherical balls. Large shot which could not be made by the shot tower was made by tumbling pieces of cut lead sheet in a barrel until round.
The "wind tower" method, which used a blast of cold air to dramatically shorten the drop necessary and was patented in 1848 by the T.O LeRoy Company of New York City,  meant that tall shot towers became unnecessary, but many were still constructed into the late 1880s, and two surviving examples date from 1916 and 1969. Since the 1960s the Bliemeister method has been used to make smaller shot sizes, and larger sizes are made by the cold swaging process of feeding calibrated lengths of wire into hemispherical dies and stamping them into spheres.