Now that guns can kill hundreds in minutes, Supreme Court should rethink the rights question

The U.S. Supreme Court is shown June 21, 2021 in Washington, DC.

Jennifer Tucker is an associate professor of history at Wesleyan University, Vice President of the Association of Firearms History & Museums, and co-editor of "A Right to Bear Arms? The Contested Role of History in Contemporary Debates on the Second Amendment." The views expressed here are her own. Read more opinion on CNN.

(CNN)This fall, the US Supreme Court will decide New York State Rifle and Pistol Association v. Kevin Bruen, a case that may result in vastly expanded rights to carry firearms in public. In doing so, the Court will need to grapple with a key question that, until now, has been left unanswered in the Second Amendment debate: Are there any limits to the type of firearm that can be carried outside of the home?

In the pivotal 2008 case District of Columbia v. Heller -- which recognized the Second Amendment as an individual right to own a gun at home for self-defense -- the Court admitted the existence of different categories of weapons, while conceding that "dangerous or unusual weapons" could be regulated. But it did not define what constitutes a "dangerous or unusual" weapon, nor recognize that there are different degrees of danger within the category of firearms.
To date, the legal debate over the Second Amendment has largely assumed that gun technology unfolds over time according to a single, linear logic, from the colonial flintlock musket to the modern AR-15. Yet the lethality of modern firearms has grown exponentially since the mid-1800s -- and this must be taken into account when considering the constitutionality of firearms regulation in a post-Heller world.
    What is needed is a common vocabulary and a shared metric for quantifying the lethality of firearms in historical terms when approaching Second Amendment policy and doctrine. Without it, the Supreme Court will not have a clear-eyed assessment of this upcoming case and the repercussions it will have on people's lives.
      Fortunately, a metric like this already exists. More than 50 years ago, the US Army commissioned a study of weapon effectiveness that sought to quantify the lethality of firearms throughout history. The designer of the study, Trevor Dupuy, was a decorated US Army colonel, a noted military historian and a founding faculty member of Harvard University's Defense Studies Program.
        In 1964, Dupuy developed the "Theoretical Lethality Index" (TLI), which calculated the lethal capacity of weapons across time. The TLI table showed how many persons a soldier with a weapon could theoretically kill in one hour.
        The study, which was prepared for the Advanced Tactics Project of the US Army Combat Developments Command, demonstrated that the TLI started increasing markedly from the mid-19th century due to improvements in range, rate of fire, accuracy, reliability and the lethality of the bullets. According to the study, a colonial soldier with an 18th century flintlock musket could kill 43 people in an hour, while a soldier in the Civil War era using a rifle with the Minie ball (a conoidal bullet adopted by the US Army in 1855) could kill 102 people in an hour. The TLI continued to rise dramatically in the late 19th century with the introduction of breech loading rifles, metal cartridges, magazines, and automatic fire machine guns. A soldier with a Springfield Model 1903 magazine rifle could kill 495 people per hour: more than a tenfold increase over the 18th century musket.
          In the 20th century, bullets became smaller and lighter, enabling soldiers to carry more, while design changes increased the damage they caused upon entering the human body. Today, the highly popular civilian AR-15 is a vastly different and substantially more lethal machine than the flintlock muskets that were in use when the Founders crafted the Second Amendment.
          Tragically, the real-world application of Dupuy's TLI is on display with every modern mass shooting. For example, in Las Vegas in 2017, a single gunman was able to kill 58 people and injure more than 850 others after firing for just 10 minutes. This would have been physically impossible for a single shooter to do in 1791.
          If the Constitution had been written in the 1880s instead of the 1780s, the Framers would have been much more aware of the pace of innovation. The Founders lived in an era when they could be forgiven for thinking that "a gun is a gun is a gun," because -- as the TLI shows -- the killing power of the basic flintlock hadn't changed in the previous 150 or so years. Dramatic changes occurred, however, during and after the Civil War.
          Given the rapid technological change we've seen in firearms over the last century and a half, the notion that guns should be viewed equally across all times and places is logically flawed: "A gun is a gun is a gun" only in the same way that an ox cart and a space rocket are both vehicles. Just as courts don't regard the bleeding and purging of patients as the gold standard of health care -- although those practices were the norm at the time of the Founders -- common sense dictates that the law must take into account technological change in firearms.
          There is room for looking at the lethality of modern firearms when considering the constitutionality of gun regulation. The court implicitly acknowledged this in its Heller decision when it stated that machine gun bans were acceptable. It's a difficult concession to explain unless the court is considering the modern capabilities of firearms outside of the historical scope of regulation.
          The issue before the Court this fall concerns the conditions under which an individual can carry a firearm publicly on their person. That question is not independent from the deadliness of the weapon that they choose to carry.
          Weapons designed with an ever-increasing capacity to kill large numbers of people in battle, with long barrels and large-capacity magazines, have no place in public spaces, supermarkets, and shopping malls -- not on the grounds of a generic right to self-defense. When it takes up this new gun case, the Court should take technological innovation into account and acknowledge that guns are now exponentially more lethal than they were when the Constitution was written.
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            The Dupuy TLI index would help with that. "This [TLI] index is useful because it allows judges to make apples-to-apples comparisons of gun regulations across centuries based on an arm's lethality," says Darrell Miller, Professor of Law and Co-Director of the Duke Center for Firearms Law.
            As Justice John Paul Stephens wrote in his dissenting opinion in the 2010 McDonald v. City of Chicago case, liberty is "on both sides of the equation" when it comes to deliberating on guns in society. "Guns may be useful for self-defense, as well as for hunting and sport, but they also have a unique potential to facilitate death and destruction and thereby to destabilize ordered liberty," Stephens wrote. "Your interest in keeping and bearing a certain firearm may diminish my interest in being and feeling safe from armed violence."