Guns have been around for a long time, so it would be reasonable to assume the definition of “firearm” is well settled by now. Not so, at least legally speaking. In fact, federal law defines “firearm” multiple ways, for different purposes, and those definitions have evolved over time. They are evolving still. Earlier this month, the House passed a bill that would amend (some of) the federal definition(s) again.
The First Federal Gun Law
The first federal law to regulate firearms was the Nonmailable Firearms Act of 1927. It prohibited mailing “pistols, revolvers, and other firearms capable of being concealed on the person” but did not explicitly define “firearm.” Perhaps because it was their first attempt, Congress might have underestimated the nuance that would soon reveal itself.
Last month, just about one year shy of the law’s hundredth anniversary, the Department of Justice’s Office of Legal Counsel (OLC) opined that the Nonmailable Firearms Act was unconstitutional, at least as applied to constitutionally protected handguns. (Read on for discussion of concealable firearms that might not be protected by the Second Amendment.)
The Second Federal Gun Law
In 1934, in the wake of Prohibition, Congress passed the second federal gun law: the National Firearms Act (NFA). This time Congress explicitly defined “firearm.” Unfortunately, it used it as a bit of a term of art. Rather than mean firearm, in the general sense, the definition was highly specific and only applied to a few narrow categories of weapons, specifically: rifles and shotguns with barrels of less than 18 inches; “machine guns” (written back then as two words; watch for an upcoming post on that); silencers; and a category that would come to be known as “Any Other Weapon” or AOWs, but which doesn’t actually mean any other weapon.
In the original version of the NFA, the definition of “firearm” included “any other weapon, except a pistol or revolver, from which a shot is discharged by an explosive if such weapon is capable of being concealed on the person.” In subsequent updates to the law, “Any Other Weapon” was added as a distinct term. In practice, it includes esoteric firearms, like those disguised as other items, such as wallets, canes, a pack of cigarettes, a lighter, a knife, or brass knuckles. (Courts have generally found that items regulated by the NFA are not protected by the Second Amendment, and that’s the reference OLC was making to “constitutionally protected” firearms, to distinguish common handguns from these.)
Later versions of the NFA also updated the definitions for “machinegun” (now one word); added a category called “destructive device”; changed the minimum barrel length for regulated rifles; and distinguished short-barreled shotguns and rifles from weapons made from shotguns and rifles. (Hint: shotguns and rifles are intended to be fired from the shoulder; remove the stock and they are no longer intended to be fired from the shoulder. Ergo, a weapon made from….) But in the eyes of the law, all the items in these categories are simply: “firearms.”
The Third and Fourth Federal Gun Laws
Then, in 1938, Congress passed the Federal Firearms Act (FFA). Once again it included a definition for “firearm,” but it was very different than the definition of “firearm” in the NFA. The definition in the FFA broadly covered “any weapon, by whatever name known, which is designed to expel a projectile or projectiles by the action of an explosive”; and it also included silencers. The term encompassed common firearms, like pistols, revolvers, shotguns, and rifles. In 1968, the Gun Control Act (GCA) would replace the FFA and expand the definition even further, to include the “frame or receiver” of a firearm.
Antique Firearms
The GCA also specifically exempted “antique firearms” from the definition of firearm, thereby freeing them from federal regulation. It defined an antique firearm as “any firearm (including any firearm with a matchlock, flintlock, percussion cap, or similar type of ignition system) manufactured in or before 1898.” (It is unclear to me why “in or before 1898” instead of just “before 1899.” That’s lawyers for you, I suppose.) The definition also included any replica of this type of firearm, even if made after 1898.
The Knight Disc Rifle
In the 1980s, a new type of muzzleloading firearm that used an “inline” ignition system was invented. Modern Muzzleloading, Inc. soon began selling the Knight Disc rifle, which used an inline system with a ‘primer’ ignition (rather than just a percussion cap). The manufacturer still took the position, however, that it was a “similar type of ignition system” mentioned in the legal definition of antique firearm, and therefore not a “firearm” under the GCA. The Bureau of Alcohol, Tobacco and Firearms (ATF) disagreed. It classified the Knight Disc rifle as a firearm, subject to all the regulations of the GCA. Litigation ensued. At a court hearing on July 24, 1998, ATF made its case.
The manufacturer, however, did not put all its eggs in one judicial basket. It understood the power of politics. On July 28, 1998, just four days after the court hearing, Senator Chuck Grassley explained on the floor of the Senate why the definition of “antique firearm” should be changed:
In recent years, there has been a strong increase in popularity in hunting and target shooting involving muzzle loading firearms which could not have been foreseen when the current law was written. As in any other sporting equipment, the technology was refined to provide safer and more reliable equipment, much like the compound bow evolved from the original long bow. Most states now offer a muzzle loading hunting season to improve deer herd management. There have been numerous technological improvements in muzzle loading weapons, including safer propellant, safety mechanism [sic], projectiles, and ignition systems.
And one of those modern muzzleloading weapons—the Knight Disc rifle—just happened to be made in Senator Grassley’s home state of Iowa.
On August 7, 1998, the court upheld ATF’s classification, in Modern Muzzleloading, Inc. v. Magaw. The Knight Disc rifle was legally a firearm. Two months later, on Oct. 21, 1998, Congress amended the definition of antique firearmjust as Senator Grassley had proposed, to include the inline ignition system. The Knight Disc rifle was no longer legally a firearm.
Axon’s Taser 10
Axon is the maker of the popular line of “Conducted Electrical Weapons” (CEW) known as Tasers. Early versions of the device used compressed gas to discharge probes connected by wires to incapacitate a target through the use of electricity. It’s latest model (the Taser 10), however, uses gunpowder to expel the probes. Recall that the GCA’s definition of firearm includes “any weapon… designed to expel a projectile or projectiles by the action of an explosive.” That fits.
Not surprisingly, ATF classified the Taser 10 as a firearm. Axon disclosed this in an SEC filing. That means Axon must maintain a Federal Firearms License (FFL), comply with all the GCA’s regulations, and pay excise taxes on each device it manufacturers. Its customers must also go through the same process to purchase the Taser 10 that they would go through to buy a traditional firearm. That adds cost and risk and narrows the market of potential buyers.
(Re)Enter Congress
Echoing the journey of the Knight Disc rifle, on February 9, 2026, the House passed H.R.2189, the Law-Enforcement Innovate to De-Escalate Act. If it becomes law, it will amend the definition of firearm in the GCA at 18 U.S.C. § 921(a)(3). Specifically, where the statute excludes “antique firearm” from the definition, the law will add “or a less-than-lethal projectile device” to that exception. It will make a similar amendment to the definition in the National Firearms Act. (The Innovate Less Lethal to De-Escalate Tax Modernization Act was included in H.R. 2189.)
The law will also add a definition of ‘less-than-lethal projectile device’ at the end of 18 U.S.C. § 921 and describe it to mean a device that is not intended to use common ammunition or “any other projectile at a velocity exceeding 500 feet per second.” According to the Taser 10 spec sheet, it discharges its probes at 205 feet per second.
In a discussion on the House floor on February 12, 2026, Representative Fitzgerald said:
When the Gun Control Act of 1968 was enacted more than 50 years ago, it was not written with the intent to regulate less-lethal projectile devices such as tasers. Unfortunately, if a taser or other device uses an explosive propellant to discharge the projectile, the ATF classifies it as a firearm. This makes it more difficult for law enforcement and public safety officers to obtain and use these devices.
There was not universal agreement, however, that another amendment to the definition of firearm was a good idea. Representative McBath worried the law “would put our law enforcement officers and so many others in great danger by giving dangerous people easy access to serious weapons” by removing these devices from the GCA. It passed the House 233 to 185 and now heads to the Senate.
A Gun by Any Other Name
It can be confusing when the law uses the same word to mean different things, then carves out exceptions, and then changes them from time to time. Add to that the various other places where federal law defines “look-alike firearm”; “unserviceable firearm”; and “loaded firearm” (to prohibit them on aircraft) and it makes a person want to shout at someone. But be careful who you shout at. Because the same law that makes it unlawful to discharge a firearm in the Supreme Court also makes it a crime to “make a harangue” there. That law does not define firearm. Nor harangue.