What this charge actually says under § 922(o)
Section 922(o)(1) of Title 18 is one sentence long: "Except as provided in paragraph (2), it shall be unlawful for any person to transfer or possess a machinegun." That is the whole ban. It applies to any person, not just people with criminal records. Unlike the felon in possession law, there is no prohibited status to prove. The prohibited thing is the item itself.
Paragraph (2) then gives two exceptions. The first covers "a transfer to or by, or possession by or under the authority of, the United States or any department or agency thereof or a State, or a department, agency, or political subdivision thereof." In plain words, this is the government exception: military, law enforcement, and other official possession under government authority. The second covers "any lawful transfer or lawful possession of a machinegun that was lawfully possessed before the date this subsection takes effect." This is the grandfather clause for machineguns that were already lawfully held when Congress enacted the ban. The statute's own notes give that date plainly: "For date this subsection takes effect, referred to in subsec. (o)(2)(B), as May 19, 1986." So the grandfather line is May 19, 1986. A machinegun lawfully possessed before that date sits under a different legal rule than anything acquired after it.
For background on where this charge sits among federal gun crimes, start with the Federal Firearms Charges hub.
What counts as a machinegun under 26 U.S.C. § 5845(b)
The ban points to a definition outside Title 18. Section 921(a)(24) says the term has the meaning "given such term in section 5845(b) of the National Firearms Act (26 U.S.C. 5845(b))." That definition reads: a machinegun "means any weapon which shoots, is designed to shoot, or can be readily restored to shoot, automatically more than one shot, without manual reloading, by a single function of the trigger."
Three phrases in that definition decide most cases. "Automatically more than one shot" is the core function test: one trigger action, multiple shots. "Designed to shoot" means a weapon built to fire automatically counts even if it is broken or missing a part at the moment. "Can be readily restored to shoot" means a weapon that fires automatically after a quick fix counts too. Each phrase widens the net beyond a working machine gun on a bench.
The definition then goes further, and this is the part that surprises people. It continues: "The term shall also include the frame or receiver of any such weapon, any part designed and intended solely and exclusively, or combination of parts designed and intended, for use in converting a weapon into a machinegun, and any combination of parts from which a machinegun can be assembled if such parts are in the possession or under the control of a person." A conversion part on its own is legally a machinegun. The small metal devices sold online as switches, sears, or conversion kits fall under this language when they are designed and intended to convert a weapon to fire automatically. The part does not need to be installed. It does not need to be inside a gun. Possession of the part can be possession of a machinegun under the law.
The Supreme Court tested the edge of this definition in 2024 in Garland v. Cargill, which asked whether a semiautomatic rifle fitted with a bump stock counts. The Court held it does not, because such a rifle "cannot fire more than one shot" with one trigger action: the trigger must release and reset between shots, so each shot comes from a separate function, and the firing is not "automatically" caused by a single trigger function in the way the statute requires. The phrases the Court focused on were "by a single function of the trigger" and "automatically." The lesson for anyone facing this charge is practical, not abstract. The definition is technical and testable. Whether an item fires more than one shot per trigger function is something experts test and argue about, and the answer is not always obvious. The Ninth Circuit's model jury instructions make the same structural point in their own way, treating section 5845(b) as the provision that defines the term for firearms cases. What the item actually does, measured against that definition, is the center of the case.
What the government must prove
The statute bans transfer or possession. The penalty provision punishes "Whoever knowingly violates subsection (a)(6), (h), (i), (j), or (o) of section 922." Put together, the case the government must build has three parts: the person transferred or possessed an item, the item was a machinegun under the definition above, and the violation was knowing. The exceptions sit alongside these elements. If the possession was under government authority, or the weapon was lawfully possessed before May 19, 1986, the ban does not apply by its own terms. Who raises an exception and how it is proven can vary, which is exactly the kind of question to put to counsel early rather than assume.
Knowledge deserves emphasis because it is where many of these cases are won or lost. Conversion devices are small, often no bigger than a coin, and they arrive by mail in unmarked packages. The government must still tie the item to the person knowingly: that the person knew they had it and knowingly transferred or possessed it. A part found in a shared car, a package ordered on someone else's account, or a borrowed gun the borrower never fired all raise the same question from different angles. What did this person actually know. Because your own statements are the government's favorite proof of knowledge, what you say after an arrest or during an ATF visit can decide this issue before a lawyer ever sees the file.
Courts break this charge down into formal elements for juries. The Fifth Circuit's pattern jury book, for example, contains a dedicated instruction numbered 2.43I titled Possession of a Machinegun, listed under sections 922(o)(1) and 924(a)(2), and its firearms commentary discusses the section 5845 definition at length. Other circuits word their instructions differently, so treat any single circuit's formulation as an example of how courts structure the charge, not a nationwide script. Your district's version is what matters at trial.
Penalties for a § 922(o) charge: the maximum, the nearby minimums, and what they are not
For a knowing violation of section 922(o), the statute provides: "Whoever knowingly violates subsection (a)(6), (h), (i), (j), or (o) of section 922 shall be fined as provided in this title, imprisoned not more than 10 years, or both." Ten years is the ceiling. It is the most the law allows for this charge, not a forecast of any particular sentence. There is no mandatory minimum in this charge itself. A first case with one weapon and no criminal history does not carry a required prison term under this statute.
Two nearby laws can change that picture sharply, and both involve machineguns specifically. Under section 924(c), which punishes using, carrying, or possessing a firearm during and in relation to a federal crime of violence or drug trafficking crime, the penalty jumps when the gun is a machinegun: where the firearm "is a machinegun or a destructive device, or is equipped with a firearm silencer or firearm muffler, the person shall be sentenced to a term of imprisonment of not less than 30 years." That 30-year minimum runs on top of the punishment for the underlying crime and cannot run at the same time as any other sentence. And for a repeat section 924(c) violation, "if the firearm involved is a machinegun or a destructive device, or is equipped with a firearm silencer or firearm muffler," the sentence is "imprisonment for life." These are not part of the machinegun possession charge. They are separate charges that can be added when a machinegun shows up alongside drugs or violence. A gun found near drugs can therefore produce both a possession case and a far more serious use case. See Firearm in Furtherance of Drug Trafficking for the other half of that pair.
Say this plainly because it matters: every penalty number on this page is a statutory limit, a mandatory floor under a different statute, or a guideline figure used in the calculation, such as a base offense level or a level increase. None of them predicts your sentence. Judges weigh the guideline range against the facts, the history, and the purposes of sentencing. The facts of a case change everything, which is why general pages like this one cannot substitute for advice about your record and your facts. The Federal Sentencing page explains how that process works.
How the guideline works: section 2K2.1
Most machinegun cases are sentenced under section 2K2.1 of the Guidelines Manual, titled Unlawful Receipt, Possession, or Transportation of Firearms or Ammunition. The commentary to that guideline lists sections 922(a) through 922(p) among the statutes it covers, which includes section 922(o). The guideline starts with a base offense level, then adds specific enhancements. Understanding its shape helps you understand what your lawyer is fighting about.
The starting point for a machinegun case is higher than for an ordinary gun case. Level 18 applies where the offense involved a firearm described in section 5845(a), and section 5845(a) expressly lists a machinegun among the firearms it covers. In the guideline's own words: "18, if the offense involved a firearm described in 26 U.S.C. § 5845(a)." That means a machinegun case starts at level 18 even with no criminal record at all. Criminal history pushes the start higher: level 20 with one prior felony conviction for a crime of violence or a controlled substance offense, level 22 where that history combines with this kind of weapon, and levels 24 and 26 with two such priors. The weapon type and the record multiply each other.
Then comes the enhancement written for exactly this problem. Subsection (b)(5) of the guideline adds levels for machinegun conversion devices: where the defendant "possessed four or more machinegun conversion devices," or "transferred or sold any machinegun conversion device" to another person, or attempted or conspired to do so, the level rises by 2, and where the defendant "possessed 30 or more machinegun conversion devices, increase by 4 levels." The guideline defines the term for its own purposes as "any part designed and intended solely and exclusively, or combination of parts designed and intended, for use in converting a weapon into a machinegun," tracking the statute. Note what this means in practice. Selling a single switch can add levels even without a large stash, and a box of thirty or more triggers the larger increase. The combined increases from the firearm count, stolen gun, and conversion device provisions cannot exceed level 29, except in the rocket and missile category, which caps how high these stack.
Several general enhancements hit machinegun cases hard as well. Where the offense involved three or more firearms, the guideline states: "If the offense involved three or more firearms, increase as follows," with a table running from 2 extra levels for 3 to 7 guns up to 10 extra levels for 200 or more. Any stolen firearm adds 2 levels, and a firearm with a serial number altered so the original information cannot be read adds 4 levels. A defendant who used or possessed a firearm "in connection with another felony offense" receives 4 extra levels, rising to level 18 at a minimum if the calculation comes out lower, which is common when the gun is found alongside drugs. And the cross reference provides that where the gun was used in connection with another offense, the court applies the guideline for that other offense when it produces a higher level, so a possession case can be sentenced as something more serious if the facts support it.
One safety valve is closed to these defendants. A person who possessed everything purely for lawful sporting purposes or collection can otherwise drop to level 6, but that reduction is unavailable to anyone whose case falls under the higher base levels, described as "other than a defendant subject to subsection (a)(1), (a)(2), (a)(3), (a)(4), or (a)(5)." Because a machinegun case starts at level 18 under subsection (a)(5) at the lowest, the sporting collection reduction does not apply. A hunter's safe full of ordinary sporting guns is one thing. A machinegun or a conversion device is another, and the guideline treats it that way.
Defenses that actually arise under this statute
Every case is different, but defenses in machinegun cases cluster around a short list. Each one attacks a specific part of the charge, which is what makes them unique to this statute rather than generic criminal defense.
Attack the definition. The item must actually meet section 5845(b). Semiautomatic weapons that need a separate trigger function for each shot are not machineguns, as Cargill confirms for bump-stock-equipped rifles. Malfunctioning guns that double fire because they are broken, weapons that cannot be readily restored to automatic fire, and devices that only help a shooter pull the trigger faster all raise definition fights. These disputes are technical. They turn on expert testing of the actual item, not on descriptions in a report. An independent test of what the item does, measured against the single function language, is often the most important defense work in the case.
Raise an exception. Official possession under government authority is outside the ban by its own text, which matters for military members, law enforcement, and contractors whose duties involve these weapons. The pre-1986 grandfather clause protects machineguns lawfully possessed before May 19, 1986, but the paperwork has to support it: registration history, transfer records, and proof of lawful possession. Claims about either exception need documents, not memories.
Attack knowledge and possession. The violation must be knowing. A small part in a shared car, a package someone else ordered, a storage unit several people used, or a gun borrowed without ever firing it can all weaken the link between the person and the item. Mere nearness to someone else's conversion device is not enough. If officers found the item through a questionable stop, search, or package opening, a suppression motion can remove it from the case entirely.
Argue the wrong statute. A paperwork failure, such as possessing an NFA firearm that simply is not registered to you, may fit the registration offense rather than the machinegun ban. The registration law punishes anyone who chooses "to receive or possess a firearm which is not registered to him in the National Firearms Registration and Transfer Record," with its own penalty of a fine up to 10,000 dollars, up to ten years, or both. Registration problems and banned-item problems are different accusations with different defenses, and prosecutors sometimes charge both to see what sticks. Making the government prove the right statute, rather than blurring the two, is real defense work. The NFA Firearms and Unregistered Firearm pages cover the registration side in detail.
Challenge the testing and the search. Machinegun cases often begin with ATF testing of a seized item and with searches of homes, cars, phones, and packages. Each step has rules. How the item was test fired, whether the test reflected the item as seized, and whether each search was lawful are all open to challenge. If federal agents are involved, read about ATF investigations and get counsel before deciding where and how to engage.
How this charge differs from its closest neighbours
Federal gun law stacks several overlapping crimes, and confusing them is easy. Three distinctions matter most.
Possession of a banned item versus possession of an unregistered item. Section 922(o) bans machineguns for almost everyone, with only the government and pre-1986 exceptions. Section 5861(d) punishes receiving or possessing an NFA firearm, which includes machineguns, silencers, short barrel rifles, and destructive devices, that is not registered to the possessor. A post-1986 machinegun cannot be registered into legality, so the two charges overlap but accuse different things: one says the item is forbidden, the other says the paperwork is missing. Both carry up to ten years, and both are usually sentenced under the same guideline, but the defenses differ. Grandfather arguments belong to the first. Registration records belong to the second.
Possession versus use in a violent or drug crime. Section 922(o) punishes having or moving the item. Section 924(c) punishes using, carrying, or possessing it in connection with a federal crime of violence or drug trafficking crime, with the 30-year minimum and possible life term described above. A machinegun in a closet and a machinegun carried during a drug deal are different cases with different exposure, even though the same physical gun is involved.
Federal versus state. Many states have their own machinegun bans, and the same arrest can draw attention from both systems. Federal prosecution tends to follow when there is a separate federal interest: online or interstate purchases, packages crossing state lines, prior federal convictions, a connection to drug trafficking, or investigation by a federal agency. An internet order shipped across the country is the classic federal fact pattern, because the commerce trail is built into the evidence.
If you are facing this charge now
Do not try to explain the item away to agents or officers. Explanations become admissions about knowledge and possession, the two things the government most needs from your mouth. Do not consent to searches, do not write statements, and do not discuss the case with anyone but your lawyer, including on jail calls. Do not test fire the item, modify it, sell it, give it away, or destroy it either. Each of those acts can create new charges or destroy evidence your lawyer needs.
Gather paperwork instead. Order confirmations, shipping records, registration forms, inheritance papers, trust documents, military or law enforcement authorizations, and anything showing when and how the item entered your life are the raw materials of the defenses above. If the item belonged to someone else or sat in a shared space, write down privately, for your lawyer only, who had access to it and when.
Then get an assessment of the three questions that drive every one of these cases: does the item actually meet the machinegun definition, does an exception cover your situation, and can the government prove you knowingly had it. Everything else, from negotiation to motions to sentencing preparation, flows from those answers.
This page is general information, not legal advice. The statutes, the guideline, and the case cited here are starting points. Your facts, your record, and your district decide what they mean for you.