You’ve likely seen some rendering, either in photos, artwork, or film, of musket-era soldiers making their own ammunition by melting and forming lead balls in molds by the fireside—but have you ever wondered how smaller lead balls for shot were produced, or mass produced for that matter, in pre-industrial times for muskets and shotguns? It’s likely not the process you imagined.

While modern ammunition manufacturing is a precise process with extremely tight tolerances, back in the day, when the breadth of ammo choices consisted of different-sized lead spheres, ammunition manufacturers relied on decidedly low-tech, but effective, shot towers, invented by William Watts of Bristol, England and patented in 1782.

Here’s how a shot tower worked: an actual tower was built and at the top, lead was heated until molten. it was then dropped through a copper sieve down through the tower below.

Surface tension caused the liquid lead to form tiny spheres, which would then solidify as the droplets fell and were partially cooled by the air, allowing them to retain their shape. The spheres were fully cooled when caught at the bottom of the tower in a water-filled basin.

Once cooled, the balls would be checked for roundness and sorted by size. Anything that wasn’t spherical was remelted. The useable shot balls were then polished with graphite to lubricate them and prevent oxidation.

For larger shot sizes, a copper sieve with bigger holes was used, but the maximum size was limited by the height of the tower, since larger droplets of lead must fall farther to cool.

According to wikipedia, a shot tower with a 40-meter drop can product #6 shot (about 2.4mm diameter) while an 80-meter drop can produce #2 shot. Larger shot sizes were made by tumbling pieces of cut lead sheet in a barrel until the soft metal was round.

Before shot towers, the only way to make small shot was to cast it in moulds, a expensive and time-consuming process, or to drip molten lead into water barrels, which produced shot that wasn’t perfectly round.

In 1848, the T.O. LeRoy Company of New York came along with the “wind tower” method, which used a blast of cold air to shorten the necessary height of the drop, meaning taller shot towers became obsolete and larger shot could be produced this way.

The Bliemeister method) has been used to make smaller shot sizes since the 1960s. Larger shot is now produced through the cold swaging process of feeding calibrated lengths of wire into hemispherical dies and then stamping them into spheres.

Though they have been obsolete since the middle of the 19th century, there are still a number of standing shot towers around the world, though none are in use. This story from atlasobscura.com features the location and photos of 10 surviving shot towers, including the long-unused building housing the Remington Shot Tower in Bridgeport, Connecticut; the Cheese Lane Shot Tower in Bristol, UK; the Phoenix Shot Tower in Baltimore, Maryland; and the Sparks Shot Tower in Philadelphia. The oldest and tallest shot tower is located in Taroona, Australia.