In this piece
- The statutory definition of a firearm reaches the frame or receiver by itself
- Under title 18, any gun made in or before 1898 falls outside the definition
- The design test does the work for rifle, shotgun and handgun
- The short-barreled categories are settled with a tape measure
- The National Firearms Act uses the word firearm to mean eight specific things
- A federal definition decides federal questions and stops there
Congress did not use the ordinary meanings of these words. It wrote definitions of its own, in 18 U.S.C. § 921 and 26 U.S.C. § 5845, with one registration provision at 26 U.S.C. § 5841.
The statutory definition of a firearm reaches the frame or receiver by itself
Start with the term the rest of federal gun law hangs on. The definition at 18 U.S.C. § 921(a)(3) has four parts. The first is “any weapon (including a starter gun) which will or is designed to or may readily be converted to expel a projectile by the action of an explosive”. The second is “the frame or receiver of any such weapon”. The third and fourth are “any firearm muffler or firearm silencer” and “any destructive device”.
Subparagraph (B) is the part that surprises people. A frame or receiver is a firearm on its own, with nothing attached.
Subparagraph (C) reaches a component most people call by another name. The statute’s words are “firearm silencer” and “firearm muffler”. Section 921(a)(25) defines both as a device “for silencing, muffling, or diminishing the report of a portable firearm”. The same paragraph reaches “any combination of parts” intended for assembling one, and “any part intended only for use in such assembly or fabrication”. Everyday speech has settled on a third word.
Ordinary speech sorts guns into categories the statute never names. That gap is worked through in a separate piece on “assault rifle” and AR-15, and this piece leaves the pair there.
Under title 18, any gun made in or before 1898 falls outside the definition
The definition closes with one short sentence: “Such term does not include an antique firearm”. The definition it points at is § 921(a)(16).
Subparagraph (A) covers any firearm “manufactured in or before 1898”. It names matchlock, flintlock and percussion cap ignition among others. Subparagraph (B) covers replicas of those, on conditions about the ammunition a replica takes. Subparagraph (C) covers muzzle loading rifles, shotguns and pistols designed to use black powder or a black powder substitute. Those must also be unable to use fixed ammunition.
Subparagraph (C) then carves things back out of itself. It excludes any weapon incorporating a firearm frame or receiver. It excludes a firearm converted into a muzzle loading weapon.
One term, two titles, two texts. Title 26 defines “antique firearm” again, and more narrowly, at 26 U.S.C. § 5845(g). There the date of manufacture is not enough on its own. A gun designed for conventional centerfire fixed ammunition still counts, unless that ammunition is no longer made and is not readily available. A citation to one is not a citation to the other.
The design test does the work for rifle, shotgun and handgun
Three definitions share a formula. A rifle, under § 921(a)(7), is “designed or redesigned, made or remade, and intended to be fired from the shoulder”. It is made “to fire only a single projectile through a rifled bore for each single pull of the trigger”. A shotgun, under § 921(a)(5), repeats the shoulder language. The definition substitutes “a smooth bore” and “either a number of ball shot or a single projectile”.
The formula asks what the object was designed, made and intended to be. It does not ask what the object looks like.
A handgun sits on a different axis. Under § 921(a)(30) a handgun “has a short stock and is designed to be held and fired by the use of a single hand”. Subparagraph (B) adds “any combination of parts” from which such a firearm can be assembled. Check that paragraph number before you cite it. Section 921(a)(29) defines a different term, “semiautomatic rifle”.
The short-barreled categories are settled with a tape measure
Most legal tests ask for judgement. These two ask for a ruler. A short-barreled rifle, under § 921(a)(8), has “one or more barrels less than sixteen inches in length”. The same paragraph reaches a weapon made from a rifle whose overall length falls under twenty-six inches. A short-barreled shotgun, under § 921(a)(6), uses eighteen inches for the barrel and the same twenty-six overall.
Paragraphs (1) through (4) of 26 U.S.C. § 5845(a) set the same thresholds on the tax side. The measurement itself asks for no judgement, though the object has to be a rifle or a shotgun first, and those two definitions are the design-and-intent tests above. A threshold written as a number does not drift, and that is the reason for writing it that way.
The National Firearms Act uses the word firearm to mean eight specific things
Section 5845 opens “For the purpose of this chapter—” and then redefines a familiar word. Under § 5845(a) a firearm is one of eight things. Four are the short-barreled categories above. The other four are “any other weapon” as defined in subsection (e), a machinegun, a destructive device, and “any silencer (as defined in section 921 of title 18, United States Code)”. The subsection then excludes antique firearms, and devices other than machineguns and destructive devices that the Secretary finds are primarily collector’s items.
The tax statute writes no silencer definition of its own. It borrows the one in title 18. Amend § 921(a)(25) and § 5845(a)(7) moves with it.
Membership in that list is what attaches consequences. The registry provision, 26 U.S.C. § 5841(a), directs a “central registry of all firearms in the United States”. Firearms the United States possesses or controls are excluded. The word firearms there carries the § 5845(a) meaning, not the ordinary one. Under § 5841(b), manufacturers, importers and makers register what they make or import. A transferred firearm is registered to the transferee by the transferor.
Set the terms side by side. Some turn on design and intent. One lays a measurement on top of a design test. One turns on nothing but membership in a list.
| Term | Statutory citation | What the definition turns on |
|---|---|---|
| Firearm | 18 U.S.C. § 921(a)(3) | Expelling a projectile by the action of an explosive; also the frame or receiver, a muffler or silencer, and a destructive device |
| Antique firearm | 18 U.S.C. § 921(a)(16) | Manufacture in or before 1898; for replicas, the ammunition; for muzzle loaders, black powder and no fixed ammunition |
| Shotgun | 18 U.S.C. § 921(a)(5) | Designed, made and intended to be fired from the shoulder; a smooth bore |
| Rifle | 18 U.S.C. § 921(a)(7) | Designed, made and intended to be fired from the shoulder; a rifled bore; a single projectile |
| Handgun | 18 U.S.C. § 921(a)(30) | A short stock, and design to be held and fired by the use of a single hand |
| Short-barreled shotgun | 18 U.S.C. § 921(a)(6); 26 U.S.C. § 5845(a)(1)-(2) | Barrels under 18 inches; or, for a weapon made from a shotgun, overall length under 26 inches |
| Short-barreled rifle | 18 U.S.C. § 921(a)(8); 26 U.S.C. § 5845(a)(3)-(4) | Barrels under 16 inches; or, for a weapon made from a rifle, overall length under 26 inches |
| Firearm silencer, firearm muffler | 18 U.S.C. § 921(a)(25) | Being a device for silencing, muffling or diminishing the report of a portable firearm |
| Firearm, in the NFA sense | 26 U.S.C. § 5845(a) | Membership in an eight-item list, with antiques and collector’s items excluded |
The short version
A federal definition decides federal questions and stops there
Each term above is defined for a stated purpose, and § 5845 says so outright: “for the purpose of this chapter”. States define several of the same words in their own codes, so a federal meaning is not a meaning everywhere. Paragraph numbers move as Congress amends: “firearm silencer” sits at § 921(a)(25) today. Repealed paragraphs leave gaps behind, which is why § 921(a)(31) is printed as repealed by Pub. L. 103-322. Open the section and read it before relying on a citation to it.
This is educational content explaining statutory terminology, not commentary on any pending legislation or litigation.
Article sources
- 18 U.S.C. § 921 — Definitions (Legal Information Institute, Cornell Law School)
- 18 U.S.C. 921 — Definitions (Office of the Law Revision Counsel, United States Code, prelim edition)
- 26 U.S.C. § 5845 — Definitions (Legal Information Institute, Cornell Law School)
- 26 U.S.C. § 5841 — Registration of firearms (Legal Information Institute, Cornell Law School)
