Reading a battlefield bullet: a rifling database for 788 historic firearms

A bullet dug out of a battlefield usually tells an archeologist one thing: its calibre. That narrows the gun down to dozens of possibilities, and it leaves the most interesting questions — who was standing where, with what weapon — unanswered. A National Park Service–funded project set out to get more out of the same lead. The result is a database of the rifling of 788 firearms made before 1900, built so that the marks on a fired bullet can point to a type of gun, a model, or even a maker.

A barrel leaves its signature

A rifled barrel has spiral ridges cut along its inside, the lands, with grooves between them. They spin the bullet so it flies true, and in doing so they press their pattern into its side. How many lands and grooves there are, how wide each is, and whether the spiral turns left or right all varied between gunmakers and models in the nineteenth century. A fired bullet carries those measurements with it.

For each of the 788 guns the database records:

A researcher who measures a recovered bullet can look it up and identify the gun, or at least narrow the list. Applied across a site, that can show which arms were really used there, how troops were deployed, and in some cases how small units moved during a fight — read from physical evidence rather than from what the records say should have been carried.

How the measurements were taken

The rifling was recorded by taking casts of each barrel's lands and grooves with forensic casting technology, accurate to a microscopic level. The plan was to link a 3D scan of every cast to the database, but the scans turned out not to show enough detail to compare. Ordinary digital photography and panoramic photography were tested instead.

Firing pins and cannon

Two further sets of evidence came out of the work. The shape of a firing pin, which varied widely until late in the nineteenth century, leaves its own mark on a fired metallic cartridge; the project documents those shapes for pre-1900 guns, so a spent case can point to a gun type too. And rifling on artillery was recorded where the chance arose — Civil War, American Indian War and Spanish–American War pieces — so that a driving band or sabot from a fired shell might identify the cannon that fired it.

Sources

Douglas D. Scott, Colorado Mesa University, Historic Rifling Data Characteristics: Using Forensic Techniques to Further Archeological Inquiry into Firearms Use, a report under grant P17AP00228 from the National Center for Preservation Technology and Training, part of the National Park Service; published by the National Park Service, a work of the United States government in the public domain. The report's contents are the author's responsibility, not the Park Service's.