Shot tower

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A shot tower is a tower designed for the production of shot balls, which were used for projectiles in firearms. In a shot tower, lead is heated until molten, then dropped through a copper sieve high inside the tower. The liquid lead solidifies as it falls and by surface tension forms tiny spherical balls. The partially cooled balls are caught at the floor of the tower in a water-filled basin.<ref>http://www.uh.edu/engines/epi422.htm</ref> 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.<ref>http://www.madsci.org/posts/archives/may2001/991166342.Eg.r.html</ref> 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 further to cool. A polishing with a slight amount of graphite is necessary for lubrication and to prevent oxidation.

Shot towers replaced the earlier techniques of casting shot in molds, 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 were made by tumbling pieces of cut lead sheet in a barrel until round.<ref>http://150.theage.com.au/view_bestofarticle.asp?straction=update&inttype=1&intid=705</ref> Shot towers were replaced by the "wind tower" method by the end of the 19th century, which used a blast of cold air to dramatically shorten the drop necessary.<ref>http://www.traphof.org/shot-towers-2/shot-towers-page-1.htm</ref> Today the Bliemeister method is 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.<ref>http://www.findarticles.com/p/articles/mi_m0BQY/is_4_49/ai_98124187</ref>

The tallest shot tower ever built still stands in the Melbourne, Australia suburb of Clifton Hill. This brick structure was built in 1882 and is 80 metres or 263 feet high to the top of the small chimney.

A contrasting shot tower is the Wythe County, Virginia tower, whose construction began around 1800 in a rural area. It was constructed of stone with walls 2.5 feet thick, as it was not practical to use brick in that region for such a large structure. It was built at the edge of a cliff and utilized a subterranean tunnel to double the overall height the lead would drop.

Other shot towers include:

Phoenix Shot Tower at Baltimore, Maryland, USA
Remington Shot Tower, Bridgeport, Connecticut, USA
Drochtersen Shot Tower at Drochtersen, Germany
Dubuque Shot Tower, Iowa, USA
Peters Shot Tower, Kings Mills, Ohio, USA
Coops (Melbourne Central) Shot Tower, Melbourne, Australia
Clifton Hill Shot Tower, Melbourne, Australia
Winchester Shot Tower, New Haven, Connecticut, USA
Sparks Shot Tower, Philadelphia, Pennsylvania, USA - America's first shot tower built in 1808.
Wythe County Shot Tower, Virginia, USA
Taroona, Hobart, Australia
Crane Park, Twickenham, UK
Thomas H Selby Shot Tower, San Francisco, California, USA
Cheese Lane Shot Tower, now part of a office development called Vertigo in Bristol, England. this was the reinforced concrete tower built to replace the very first shot tower built in Redcliffe by William Watts

None of these are still in use, although some are open to the public. The Wythe County Shot Tower is part of a state park and is open to the public during the tourist season.