What Is an NFA Firearm? Categories, Registration & Penalties

An NFA firearm is a weapon or accessory regulated under the National Firearms Act of 1934, codified in Chapter 53 of the Internal Revenue Code. The law covers six categories: machine guns, short-barreled rifles, short-barreled shotguns, suppressors, destructive devices, and a residual class called “any other weapon.” Every item in these categories has to be entered in a federal registry, and in almost every case you need an approved application and background check before you can take possession.¹

The Six Categories

The NFA uses “firearm” as a term of art. It does not mean any gun. It means an item that meets one of six precise definitions.¹

Machine guns. Any weapon that fires more than one round with a single trigger pull. The definition also reaches the frame or receiver of such a weapon, conversion parts that would turn a semi-automatic into a fully automatic, and any collection of parts from which a machine gun could be assembled.
Short-barreled rifles. A rifle with a barrel under 16 inches or an overall length under 26 inches. A weapon “made from a rifle” that hits either measurement qualifies too.
Short-barreled shotguns. A shotgun with a barrel under 18 inches or an overall length under 26 inches, plus anything made from a shotgun that meets those numbers.
Suppressors. Any device that reduces the sound of a gunshot, and any combination of parts intended to build one.
Destructive devices. Explosive ordnance such as grenades, bombs, and mines, and any firearm with a bore diameter over half an inch. Most conventional shotguns are excluded as suitable for sporting purposes.
Any other weapon (AOW). A catch-all for concealable firearms that don’t fit the other classes. Pen guns, cane guns, smooth-bore pistols made to fire shotgun shells, and firearms disguised as everyday objects all land here.

These measurements are enforced literally. Cutting even a fraction of an inch off a rifle barrel can reclassify a legal firearm as an NFA item, and possession without prior paperwork is a federal felony.

Machine Guns Are a Special Case

The Hughes Amendment, added by the Firearm Owners Protection Act of 1986, made it a federal crime to transfer or possess any machine gun that was not lawfully owned before the law’s effective date.² No new machine guns can enter the civilian market. The only transferable ones are those manufactured and registered before May 1986, and that pool only shrinks as guns are destroyed or rendered inoperable.

The frozen supply pushes prices for even basic transferable machine guns into the tens of thousands of dollars. Government agencies and dealers holding a special occupational tax license operate under different rules, but for civilians the ceiling is set. Violations carry up to 10 years in prison.³

The Tax Stamp Today

The NFA’s original enforcement lever was a $200 tax on making or transferring a regulated firearm, a prohibitive sum in 1934 that Congress never indexed to inflation. For most of the law’s history that tax applied across the board. Recent legislation changed the picture: the making and transfer tax for suppressors, short-barreled rifles, short-barreled shotguns, and AOWs is now $0.⁴⁵

The $200 tax still applies to machine guns and destructive devices. Because civilians can only buy pre-1986 machine guns and destructive device transfers are uncommon, most people going through the NFA process today owe no federal tax at all. Registration, application, and background check requirements still apply regardless of the tax amount.

How You Register an NFA Firearm

Every NFA firearm has to appear in the National Firearms Registration and Transfer Record, the central database the ATF maintains.⁶ Two forms handle most registrations:

ATF Form 1 (5320.1) is used when you intend to make an NFA firearm yourself, for example by assembling a suppressor or shortening a rifle barrel below 16 inches.⁷
ATF Form 4 (5320.4) is used to transfer an existing NFA firearm, typically from a licensed dealer to a buyer.⁸

Both forms require fingerprint cards (FD-258), a passport-style photograph, and detailed information about the firearm including manufacturer, model, serial number, and barrel and overall length. You also have to send a copy of the application to your local Chief Law Enforcement Officer. That is a notice requirement only. The CLEO has no authority to block the application.⁹

You cannot take possession of the firearm until the ATF approves the application.¹⁰ Approval comes back as a document bearing a tax stamp, even when the tax amount is $0. Keep that document accessible whenever the item is with you. Most applicants now file electronically through the ATF’s eForms portal, and current processing times run considerably shorter than the year-plus waits that used to be routine for paper filings.¹¹ The ATF will deny an application if the transfer would place the applicant in violation of law, most often for a disqualifying criminal record, a pending charge, or the item being illegal in the applicant’s state.

Individual Registration vs. a Gun Trust

You can register an NFA firearm to yourself or to a legal entity such as a trust or corporation. Individual registration is simpler on paper. You are the only person who can lawfully handle the firearm, and when you die the executor has to work through ATF paperwork during estate settlement.

A trust changes both points. Every trustee named in the trust can legally possess and use the registered items without the original owner being present, and at death the items pass to named beneficiaries through the trust without a new transfer application or additional tax. The tradeoff is administrative. Setting up a trust takes upfront effort and usually a legal fee, and every “responsible person” on the trust (anyone with authority to possess or direct the use of the firearms) must submit fingerprints, a photograph, and background information on ATF Form 5320.23 with any Form 1 or Form 4 filed by the trust.

Rules Once You Own It

Only the person or entity on the approved registration document can lawfully possess the firearm. Possessing an unregistered NFA item, or one registered to someone else, is a standalone federal crime.¹²

Constructive Possession

This is where people who share a home run into trouble. “Constructive possession” means having the ability to access and control a firearm even if you are not holding it. If your spouse or roommate knows the safe combination and can reach your registered suppressor or SBR whenever they want, a prosecutor could argue they constructively possess an NFA item not registered to them. The safest approach is to store NFA firearms so only the registered owner, or authorized trustees, can reach them. This is one of the strongest practical reasons to use a trust when other adults live in the house.

Interstate Transport

Taking a machine gun, short-barreled rifle, short-barreled shotgun, or destructive device across state lines requires advance ATF approval on Form 5320.20, whether the trip is temporary or a permanent move.¹³ Suppressors and AOWs are not on that list. You still need to confirm the destination state allows the item, but you do not need separate travel authorization for those two categories.

Engraving Homemade Items

If you make an NFA firearm under an approved Form 1, federal regulations require you to permanently mark it with your name (or the trust name), the city and state where it was made, a unique serial number, and the caliber or gauge. The markings must be at least .003 inches deep, and the serial number must be at least 1/16 inch tall and visible without disassembly.¹⁴ Most people hire a professional engraver because those tolerances are hard to hit with hand tools. Do this before assembling or using the item. Possessing an unidentified NFA firearm is a separate federal offense even if your Form 1 is approved.¹²

State Law Can Still Ban What Federal Law Allows

Federal registration does not override state law. Suppressors are prohibited in a handful of states. Short-barreled rifles and shotguns are restricted or banned in some jurisdictions. Machine gun ownership beyond the pre-1986 supply faces additional state permit requirements or bans in numerous states. The District of Columbia prohibits every NFA category except standard firearms. An approved ATF form does not protect you from state prosecution if your state bans the item. The ATF will deny a transfer application if the item would be illegal at your address, but this is not a failsafe worth relying on. Check state and local law before starting the federal process.

Penalties

The NFA’s own penalty provision allows fines up to $10,000, imprisonment up to 10 years, or both, for any violation of the chapter.¹⁵ General federal sentencing statutes can push fines higher in practice, and separate penalties under 18 USC 924 apply to related offenses like violating the machine gun ban.³

The prohibited acts that trigger those penalties cover a wide range of conduct: possessing an unregistered NFA firearm, transferring one outside the proper process, making one without approval, tampering with serial numbers, transporting an unregistered item across state lines, and making false statements on any NFA form.¹² A conviction also makes you a prohibited person under federal law, permanently barring you from owning any firearm.

1
Office of the Law Revision Counsel. 26 USC 5845 – Definitions
2
Office of the Law Revision Counsel. 18 USC 922 – Unlawful Acts
3
Office of the Law Revision Counsel. 18 USC 924 – Penalties
4
Office of the Law Revision Counsel. 26 USC 5811 – Transfer Tax
5
Office of the Law Revision Counsel. 26 USC 5821 – Making Tax
6
Office of the Law Revision Counsel. 26 USC 5841 – Registration of Firearms
7
Bureau of Alcohol, Tobacco, Firearms, and Explosives. ATF Form 5320.1 – Application to Make and Register NFA Firearm
8
Bureau of Alcohol, Tobacco, Firearms and Explosives. Firearms Forms
9
Bureau of Alcohol, Tobacco, Firearms and Explosives. eForms Applications
10
Office of the Law Revision Counsel. 26 USC 5812 – Transfers
11
Bureau of Alcohol, Tobacco, Firearms and Explosives. Current Processing Times
12
Office of the Law Revision Counsel. 26 USC 5861 – Prohibited Acts
13
Bureau of Alcohol, Tobacco, Firearms and Explosives. ATF Form 5320.20 – Application to Transport Interstate Certain NFA Firearms
14
eCFR. 27 CFR 479.102 – Identification of Firearms
15
Office of the Law Revision Counsel. 26 USC 5871 – Penalties