18 USC 922(o): Machine Gun Possession, Penalties, and Defenses

Under 18 U.S.C. 922(o), it is a federal felony to transfer or possess a machine gun, punishable by up to ten years in prison.¹² The statute was added by the Firearm Owners’ Protection Act of 1986 and froze the civilian market: no machine gun made after May 19, 1986 can be lawfully owned by a private citizen. Two exceptions survive. Government agencies can possess machine guns, and any machine gun that was lawfully registered before that date can still be bought, sold, and inherited under National Firearms Act rules.

What Counts as a Machine Gun

The National Firearms Act defines a machine gun as any weapon that fires more than one shot with a single pull of the trigger without manual reloading between shots.³ The definition reaches further than the weapon itself. It covers the frame or receiver of a machine gun, any part designed exclusively to convert a firearm into a machine gun, and any collection of parts that could be assembled into one if the parts are in a person’s possession or control.

That last piece matters. Small conversion devices such as drop-in auto sears, lightning links, and “Glock switches” are themselves machine guns under federal law, whether or not they are installed in a firearm. The ATF has treated trafficking in these devices as a priority, noting that a pistol equipped with a switch can fire up to 1,200 rounds per minute.⁴ Possessing a switch carries the same exposure under 922(o) as possessing a full auto rifle.

The Pre-1986 Cutoff and Its Two Exceptions

Before 1986, civilians could register machine guns under the NFA by paying a $200 transfer tax. Subsection (o) closed that door. It makes it unlawful for any person to transfer or possess a machine gun, subject to two carve-outs.¹

The first exception covers transfers to or by the United States, any state, or any department or agency of either. Law enforcement and military entities can acquire post-1986 machine guns for official use, with the firearms registered to the agency itself.

The second grandfathers any machine gun lawfully possessed before May 19, 1986. That created a fixed and shrinking pool of transferable machine guns in civilian hands. No new ones can be added, and every one destroyed or rendered inoperable permanently reduces the supply. Prices for transferable pre-1986 machine guns run well into the tens of thousands of dollars as a result.

A narrow third category exists on the business side. Federal firearms licensees who also hold Special Occupational Taxpayer status can manufacture and possess post-1986 machine guns, but only to sell to government buyers or as demonstration samples. Getting a post-1986 dealer sales sample requires a “law letter” from a government entity expressing interest in seeing that specific model demonstrated.⁵

Buying a Pre-1986 Machine Gun

A private citizen can still legally buy a machine gun that was lawfully registered before May 19, 1986. The transfer runs through ATF Form 4, an application for tax-paid transfer and registration.⁶ The main requirements:

A $200 federal transfer tax. Machine guns still owe this tax in 2026, even though Congress recently eliminated the NFA tax for silencers and short-barreled rifles.
A completed Form 4 with fingerprint cards and photographs. An individual applicant must also obtain a certification from an appropriate law enforcement official.
Compliance with any state or local permit requirements, with a copy of the permit included in the application.
ATF approval before the seller hands over the weapon. The application is denied if possession would violate federal, state, or local law.

As of February 2026, the ATF’s average processing time for eForm 4 applications was 10 days for individual filings and 26 days for trust filings, well below the months-long waits common before the eForms system.⁷

Many buyers register through an NFA trust rather than as individuals. A trust lets multiple named trustees legally possess and transport the firearm, and it passes the weapon to named beneficiaries through the trust’s own terms rather than through probate.

Inheriting a Machine Gun

When a registered owner dies, the executor can hold the firearm during probate without triggering a “transfer” under the NFA, but a transfer application has to be filed before probate closes.⁸

If the machine gun passes to a beneficiary named in the will, the executor uses ATF Form 5, a tax-exempt transfer, and no $200 tax is owed. The application needs the executor’s appointment paperwork, the death certificate, a copy of the will, and any other documents establishing authority over the estate. If the beneficiary doesn’t want the gun and the estate sells it to an outside buyer, that sale runs through Form 4 with the standard $200 tax.

An unregistered machine gun in an estate is contraband. It cannot be registered after the fact. The executor should contact the local ATF field office to arrange abandonment.⁹ Keeping it, trying to sell it, or ignoring it exposes the executor to federal prosecution.

Penalties for Illegal Possession

A 922(o) violation is a felony with a statutory maximum of ten years in federal prison.² Fines can reach $250,000 for an individual and $500,000 for an organization under the general federal fines statute.¹⁰ Prosecutors can also bring the same conduct under 26 U.S.C. 5871, the NFA’s own penalty provision, which carries up to ten years and a $10,000 fine for possession of an unregistered NFA firearm.¹¹ Federal prosecutors sometimes charge both.

A felony conviction also strips the right to possess any firearm going forward, limits employment, and can trigger immigration consequences for non-citizens.

Mandatory Minimums Under 924(c)

The penalties escalate sharply when a machine gun is involved in a crime of violence or drug trafficking. Under 18 U.S.C. 924(c), possessing a machine gun during such a crime carries a mandatory minimum of 30 years, with no probation available, and that sentence runs consecutively to whatever the underlying crime carries.¹² A second 924(c) conviction involving a machine gun triggers a mandatory life sentence. Federal judges have no discretion to go below these floors.

Seizure and Forfeiture

Federal authorities can seize and forfeit any firearm involved in a knowing violation of the firearms laws under 18 U.S.C. 924(d).¹³ Civil forfeiture allows confiscation without a criminal charge, in which case the owner has to prove lawful possession to get the firearm back. Criminal forfeiture follows a conviction. Proceedings must be initiated within 120 days of seizure. If the owner is acquitted or charges are dismissed, the firearms must be returned unless doing so would itself violate the law.

The Knowledge Requirement and Common Defenses

Possession under 922(o) is not strict liability. The penalty statute, 18 U.S.C. 924(a)(2), requires that the person “knowingly” violates the law.² In practice, “knowingly” in federal firearms law means the person knew they possessed the item and knew its characteristics, not that they knew the item was illegal. If you know a device fires automatically, the government does not also have to prove you knew the statute prohibited it.

That still leaves room for defense in specific situations. A defendant who genuinely did not know an inherited or previously modified firearm was capable of automatic fire may have a viable knowledge defense, often supported by expert testimony from a firearms examiner. Procedural defenses tend to be the strongest: a Fourth Amendment challenge to a warrantless search or a search that exceeded its warrant can suppress the weapon as evidence, and without the weapon, the case usually collapses.

Another defense challenges whether the seized device actually meets the statutory definition of a machine gun. Where that classification is genuinely debatable, the argument has teeth. Second Amendment challenges to 922(o) have been raised repeatedly, including after the Supreme Court’s 2022 Bruen decision, and federal circuit courts have consistently rejected them.

Where the Line Sits on Accessories

Two categories of accessories have been actively litigated, and the outcomes matter for anyone deciding what is safe to own.

Bump stocks are not machine guns under federal law. The Supreme Court struck down the ATF’s 2018 rule classifying them as such in Garland v. Cargill, holding 6-3 in June 2024 that a semiautomatic rifle equipped with a bump stock does not fire more than one shot “by a single function of the trigger” because the shooter has to release and reset the trigger between each shot.¹⁴ Some states have their own bans.

Forced reset triggers followed a similar arc. The ATF originally classified specific models, including the Rare Breed FRT-15 and Wide Open Trigger, as machine guns. A federal court in Texas disagreed in 2024, and a 2025 settlement agreement between the United States and Rare Breed Triggers bars the government from enforcing 922(o) against people who possess eligible FRTs.¹⁵

The FRT settlement explicitly does not cover traditional conversion devices such as switches, drop-in auto sears, lightning links, or trigger control group travel reducers. Possessing any of those is treated identically to possessing a fully automatic firearm.¹⁵

Household Access and Constructive Possession

If you own a registered machine gun as an individual, you are the only person authorized to possess it. Giving a spouse, partner, or adult child the combination to the safe where NFA firearms are stored can expose them to constructive possession charges. Constructive possession exists when someone knowingly has the power and intention to exercise control over an item, even without physically holding it. Access to the storage location can be enough. A prosecutor does not need to prove the household member actually handled the weapon.

The practical fix is either restricting safe access to yourself alone or registering the firearm through an NFA trust that names the other household members as trustees. Trustees can legally possess, transport, and use the firearms listed on the trust.