Sorely missing from the current debate is a shared vocabulary for what the public policy and the constitutional doctrine is aiming to achieve. Terms like “common use,” “dangerous and unusual,” “lineal descendants” or “employed in civilized warfare” cannot adequately discipline doctrine or debate without some common denominator for the task. This Article suggests that focusing on lethality is one way to converge on a shared metric for the discussion.

The late Trevor N. Dupuy, a senior U.S. Army officer during World War II who later became a respected and prolific military historian, developed one such metric in the middle of the twentieth century — the Theoretical Lethality Index (“TLI”). In 1964, the United States Army contracted with Dupuy to analyze how the killing power of weapons had increased over time — he created the TLI to measure how many people a particular weapon could kill in one hour. Dupuy worked on this project for a non-partisan entity which had an interest in the accuracy and utility of his formula — the United States military. As such, Dupuy’s Theoretical Lethality Index offers a useful metric for quantifying the lethality of firearms in historical terms. His index can provide at least a starting point to construct a common scale to assess the functionality of weapons both within and across various time periods.