Key Takeaways
- The Second Amendment protects "arms," which Heller read broadly to include bearable weapons of offense or defense, not only firearms.
- Courts generally ask whether a weapon is in common use by law-abiding citizens for lawful purposes, while weapons considered "dangerous and unusual," such as machine guns, can be banned.
- In Caetano v. Massachusetts, the Supreme Court made clear that a weapon is not unprotected simply because it did not exist in 1791, and the Court has now agreed to decide whether AR-15-style rifles are protected.
The Second Amendment protects the right to keep and bear "arms." But does that mean only guns? What about stun guns, knives, nunchucks, or a samurai sword?
In this TalksOnLaw Brief, Jake Charles, Associate Professor of Law at Pepperdine Caruso School of Law and a Second Amendment scholar, explains how the Supreme Court has defined "arms," the tests courts use to decide which weapons are protected, and why the question now sits at the center of litigation over assault weapons bans.
Arms, Not Just Firearms
Professor Charles points out that the Second Amendment says "arms," not "firearms," even though public debate and many court cases treat the two as the same. In District of Columbia v. Heller (2008), the Supreme Court read the term broadly to cover bearable weapons of offense or defense, so a large category of weapons is presumptively included. He credits scholarship by Professor Eric Ruben of SMU Dedman School of Law for showing how the gun-centric focus of Second Amendment doctrine can warp our understanding. Lower courts have addressed knives and nunchucks, and some have found restrictions on them unconstitutional, including in a New York nunchucks case.
Common Use and "Dangerous and Unusual"
Two benchmarks emerge from the Court's hints, developed further in the lower courts. Weapons in common use by law-abiding citizens for lawful purposes receive protection, while weapons that are "dangerous and unusual" do not. The Supreme Court has not said whether a weapon must be both, and Professor Charles notes the courts are all over the map. Since every gun is dangerous, some suggest the real question is whether a weapon is unusually dangerous. That raises a baseline problem: an AR-15 might have seemed unusually dangerous in 1791, before repeating rifles, yet is commonplace today. The common use test also leaves open how widespread a weapon must be, whether common in one state is enough, and whether "use" means use in self-defense or simply possession, a point disputed in cases over high-capacity magazines.
Caetano and the Stun Gun Case
Professor Charles highlights Caetano v. Massachusetts (2016). Massachusetts's highest court had upheld a stun gun ban partly because stun guns were not in common use in 1791. In a short, unsigned per curiam opinion, the Supreme Court vacated that ruling, explaining that Heller rejected the idea that only weapons existing at the founding are protected, much as the First Amendment covers modern forms of communication. No justice noted a dissent. Justice Alito's longer concurrence argued it would be perverse to allow a ban on stun guns, which are less lethal than the handguns Heller protected.
What to Know Now
What Professor Charles calls the "million-dollar question" is now before the Supreme Court. After declining in 2025 to hear challenges to Maryland's assault weapons ban and Rhode Island's magazine limit, the Court in 2026 agreed to decide Viramontes v. Cook County, consolidated with a challenge to Connecticut's law and limited to whether the Second and Fourteenth Amendments protect AR-15-platform and similar semiautomatic rifles. Lower courts have largely upheld assault weapons and large-capacity magazine bans, often reasoning that these weapons are especially suited to military use or are rarely needed for self-defense, while challengers argue that millions of Americans lawfully own them for self-defense and other lawful purposes. Meanwhile, United States v. Rahimi (2024) clarified that historical analysis looks for laws consistent with the principles of the nation's regulatory tradition rather than a "historical twin." Whatever the Court decides, the common use and "dangerous and unusual" concepts Professor Charles describes will frame the outcome.
