Shot Tower- Perfect Lead Balls, Every Time
Mechanised warfare depends on cheap, easy production of the basic equipment. The success of the AK-47 has as much to do with its remarkably low cost of production and operation as anything else.
A few centuries before that; and long before Henry Ford's division of labour brought even complex petrol-driven automobiles within reach of millions; the biggest problem in armaments was the production of ammunition. In the 1700s, the pressing need was for lead shot. Shot is a group of lead spheres a few millimetres across. They could be packed into a cartridge, similar to a modern shotgun; or dumped into a cannon-like blunderbuss with enough loose gunpowder to blast it out. Lead is heavy, and each pellet of shot is small. A shotgun discharges a spray of these pellets into an expanding cone shape. Handy for hitting moderate speed targets at a moderate distance (like game birds) or for really ruining someone's day at close-quarters.
In those days, lead shot was made by casting- which is to say, pouring molten lead into tiny molds and hoping for the best. This method was laborious, but at least you got a consistent, near-spherical product— if you concentrated and knew what you where doing. The low-skilled alternative was to pour molten lead into water through a sieve. The sieve broke the streak of red-hot metal into a stream of droplets, which the water cooled into shot. This worked well, but the result was teardrop-shaped and therefore less-effective. Such shot could only be sold as a bargain-basement, cheap alternative to the real thing.
How to achieve the high-value perfect sphere with a low cost technique?
In 1775, a plumber named William Watts had a stroke of inspiration. Perhaps noticing that tear-drops are not spherical, but raindrops are; he guessed that this must have something to do with the distance they have fallen. Over a long fall, surface tension pulls the water into a perfect sphere, and the same would probably be true for liquid lead. As it turned out, lead has a very high surface tension- much higher than water. All he would have to do is make lead drops fall from high up, and he'd have perfect shot. As a plumber, he had no problem getting hold of lead in quantity- and Bristol was anyway the centre of shot production, and had been involved in the lead trade since Roman times.
Watts lived in a nondescript three-storey terrace at Redcliffe Hill in Bristol. Perhaps a little experimentation convinced him that this was not high enough for his new requirements. He began to build it higher. He added another 3 storeys, then pretty castle-like crenellations to curry favour with the neighbours. He then started to dig, and didn't stop until he hit the disused mine tunnel known as Redcliffe Caves. Down there, he installed a water tank, and cut a hole through each floor to the top. As with budget shot suppliers, he poured his lead through a sieve. Different sieves gave different shot sizes. But Watts' factory allowed each drop to fall far enough to form a perfect sphere and start to solidify before hitting the water. He patented his idea a few years later, the abstract claiming his shot was "solid throughout, perfectly globular in form, and without the dimples, scratches and imperfections, which other shot, heretofore manufactured, usually have on their surface."
History does not record the effect on the operators' health, but working in a small chamber at the top of a tower with a roiling pot of molten lead cannot have been much fun. Nevermind lead poisoning, an eye-witness account of 1883 recorded that the chamber walls were caked with with a greenish sulphur and arsenic crust. These were impurities in lead, which actually assisted in the smooth working of the process. In operation though, the observer found the process quite beautiful, saying "the molten lead is falling like a magnificent cataract of sparkling silver, while the sound from beneath, as the myriads of drops fall into the well somewhat resembles that of a distant fusillade". By this time, shot was drawn up from the water by means of a 30 foot long ladle- but the observer also spotted a small alcove at the water level in which a small boy could be stationed to check the process as it took place!.
Watts sold his business and patent, was foolish with the takings and was bankrupted. But the firm went on to become the "Sheldon, Bush and Patent Shot Company" in 1868. They continued to operate at Watts' modified home until 1968, when it was demolished for a new road scheme. The ugly, 140 foot tall replacement tower is now a listed building, but has been unused for shot since the company finally closed its doors in 1995. It's now part of an office development called Vertigo.
Market conditions were unfavorable by then- and in 1999, "Statutory Instrument 1999 No. 2170" entered law as secondary legislation under the 1990 Environmental Protection Act. It banned use of lead shot, or any shot with more than 1% lead in a wide range of circumstances.
In the meantime, hundreds of shot towers had shot up all over the world and had shot dropped down them. London had several by 1789. The USA started building their own after Thomas Jefferson's Embargo Act came into force in 1808. In some locations, disused mine shafts were used. Other shortcuts, like dropping lead through a fine water-mist or an updraft didn't work as well as a really, really tall tower. So some towers still stand in Maryland, Virginia, Connecticut, Iowa, California, Ohio, and Pennsylvania in the USA; Dorchtersen in Germany; Chester, Bristol and Twickenham in the UK, and at four sites in Australia. One of these Australian sites has been engulfed by a skeletal shopping centre facade, but it still stands proudly.
Today, shot can be made by dropping the molten metal a few inches onto an underwater ramp. It is then rounded by rolling. This "Bliemeister method" is simple enough to allow the rugged individualist to make his own shot- and perhaps to evade environmental regulations.
- No. 422, Shot Tower. John H. Lienhard. http://www.uh.edu/engines/epi422.htm
- Lead Shot Tower. http://www.ukattraction.com/west-country/lead-shot-tower.htm
- Shotgun, http://en.wikipedia.org/wiki/Shotgun
- Bristol, 1700 Onwards, http://members.lycos.co.uk/brisray/bristol/bhist6.htm
- Statutory Instrument 1999 No. 2170, http://www.opsi.gov.uk/si/si1999/19992170.htm
- The Shot Tower, http://www.americanheritage.com/articles/magazine/it/1990/1/1990_1_52.shtml
- 1883 account, http://www.bristoltours.com/text_h.htm
- strawberryfrog's Melbourne Shot Tower pictures: http://www.flickr.com/photos/strawberryfrog/112084194/