What this charge is about
Every gun made in this country or brought in from abroad by a licensed maker or importer must carry that maker or importer serial number on its frame or receiver. The statute puts it this way: licensed importers and makers "shall identify by means of a serial number engraved or cast on the receiver or frame of the weapon" each gun they make or bring in. That number is how police trace a gun. Grinding it off, punching new digits over it, or melting it past reading breaks the trace, and that is what this charge punishes.
The charge comes from 18 U.S.C. § 922(k), which reads in full:
"It shall be unlawful for any person knowingly to transport, ship, or receive, in interstate or foreign commerce, any firearm which has had the importer's or manufacturer's serial number removed, obliterated, or altered or to possess or receive any firearm which has had the importer's or manufacturer's serial number removed, obliterated, or altered and has, at any time, been shipped or transported in interstate or foreign commerce."
That one sentence holds two paths to a conviction. The first path covers moving a defaced gun across state or national lines: transport, ship, or receive it in commerce. The second path covers simply having it: possess or receive a defaced gun that, at some point in its life, traveled in commerce. Most cases take the second path, because almost every gun has crossed a state line at some point between factory and street.
Note what the charge is not. It does not ask whether you are allowed to own a gun, the way a felon in possession charge does. It does not ask whether the gun was stolen. It asks only about the number. A legally bought gun with a ground-off number can support this charge, and a stolen gun with an intact number cannot. For the wider picture of federal gun cases, start with the Federal Firearms Charges hub.
What the government must prove
A federal case must prove every element beyond a reasonable doubt. The Ninth Circuit's model jury instructions break this charge into three elements the jury must each find proven:
First, that you knew you transported, shipped, received, or possessed the gun. Second, that the gun serial number had in fact been removed, obliterated, or altered. Third, that you knew it: "the defendant knew that the serial number had been removed, obliterated, or altered."
Two points in that list surprise most people. Knowledge is one of them. The government cannot win by showing only that the number was damaged. Under the Ninth Circuit's instruction it must also show you knew about the damage. Someone who picks up a gun in the dark during a fight, or who buys a used pistol without ever looking at the frame, presents a knowledge question the jury must answer. How your circuit words this instruction may differ, so counsel checks the instruction used in your court.
The other surprise is the commerce link. For simple possession, the gun must have "at any time, been shipped or transported in interstate or foreign commerce." The words "at any time" mean the trip does not have to be recent and does not have to be yours. A pistol made in one state and found in your pocket in another satisfies the link even if it crossed the line decades ago. Where the gun was made and where it was found therefore matter, and counsel tests that proof rather than assuming it.
Punishment under § 924(a)(1)(B) if convicted
The penalty law for this charge is 18 U.S.C. § 924(a)(1)(B). It punishes anyone who "knowingly violates subsection (a)(4), (f), (k), or (q) of section 922," and the sentence for that violation "shall be fined under this title, imprisoned not more than five years, or both."
Read that sentence carefully, because each part matters to a frightened reader:
Five years is a maximum, not a prediction. The judge can impose any sentence from probation up to five years. The statute states no minimum prison term, so unlike some federal gun charges there is no floor the judge must impose.
A fine can be added to prison time or imposed on its own. The fine is set under the general fine provisions of federal law.
The gun itself is at risk. Under 18 U.S.C. § 924(d)(1), a firearm involved in a knowing violation of section 922(k) is subject to seizure and forfeiture, which means the government can take it permanently. Ammunition involved in the offense faces the same fate.
The guideline range is a starting point, not the sentence. The 2025 Guidelines Manual describes an advisory scheme: the court first calculates the guideline range and then imposes a sentence that is "sufficient, but not greater than necessary" to serve the purposes of sentencing, while the Manual reminds courts they are "not bound to apply the Guidelines" but must take them into account. How that calculation works for this charge is the next section, and how judges impose sentences generally is covered on the federal sentencing page.
None of these numbers predict your case. Two people convicted under the same statute can receive very different sentences because their histories and facts differ. The facts of a case change everything.
How the guidelines (USSG §2K2.1) treat this charge
The Statutory Index in the 2025 Guidelines Manual maps "18 U.S.C. § 922(a)–(p)" to guideline "2K2.1," so a serial-number conviction is sentenced under USSG §2K2.1, titled Unlawful Receipt, Possession, or Transportation of Firearms or Ammunition. That section sets a base offense level and then adds levels for specific facts.
The base level for a typical serial-number case is 12. Section 2K2.1(a) lists base levels from 6 to 26 depending on criminal history, prohibited-person status, and weapon type. A first-time defendant with an ordinary handgun and no aggravating history lands on subsection (a)(7): level 12. Prior felony convictions for violence or drugs, prohibited-person status, or a machinegun-type weapon can raise the base level substantially, so your history matters from the first step.
The enhancement written for this exact situation is subsection (b)(4). It provides that where "any firearm was stolen, increase by 2 levels," and where "any firearm had a serial number that was modified such that the original information is rendered illegible or unrecognizable to the unaided eye," or the defendant knew the gun carried no serial number at all, "increase by 4 levels." A scratched but readable number should not trigger that increase, because the test is illegibility to the naked eye, not any damage at all.
Here this page earns its keep, because the Manual contains a trap for the unwary that applies to this charge by name. Application Note 8(A) explains that when the base level is 12 under subsection (a)(7) and the only offense is the serial-number charge, the 4-level increase for the modified number does not apply on top, because the base level already accounts for the damaged number. Counting it again would punish the same fact twice. But the Note adds two exceptions that prosecutors use: if the gun was also stolen, the 2-level stolen increase can still apply, and if you knew the gun had no serial number at all, that separate increase can still apply. So a defaced number alone adds nothing to level 12, while a defaced number on a stolen gun can add two levels.
The Note also settles a knowledge question at sentencing that differs from the trial rule. At trial, the Ninth Circuit requires proof you knew the number was damaged. At sentencing, the stolen and modified-number increases apply on a stricter basis: "Subsection (b)(4)(A) or (B)(i) applies regardless of whether the defendant knew or had reason to believe that the firearm was stolen." In plain words, the guideline can raise your level for a ground-off number even if you never noticed it, while only the no-number-at-all increase requires proof you knew or deliberately avoided knowing.
Other facts can move the level further. Three or more guns trigger an increase that grows with the count. Using the gun "in connection with another felony offense" adds 4 levels and lifts the result to at least level 18: "If the resulting offense level is less than level 18, increase to level 18." And a narrow reduction exists for the collector: someone who possessed everything solely for lawful sport or collection, without unlawful use, can drop to level 6. The offense level then combines with criminal history to produce the guideline range the judge considers alongside everything else.
Defenses that come up under this statute
Every defense below depends on the facts. None is automatic, and none promises an outcome. They are the issues counsel examines because this statute raises them:
You did not know the number was damaged. Knowledge is an element under the Ninth Circuit's instruction, quoted above. Evidence that you handled the gun briefly, received it in the dark, or bought it without inspecting the frame can attack the claim that you knew. The government will answer with evidence like your opportunity to look, statements you made, and tools or grinding marks suggesting personal involvement. The jury decides which story fits.
The number is damaged but still readable, or the wrong marking is damaged. The charge covers the importer or maker serial number. Proof that the serial number remains legible, or that only a different stamp was scratched, cuts against both guilt and the guideline increase. The Ninth Circuit's instruction commentary treats a number as altered when it was changed in a way that makes it appreciably harder to read, so a merely worn number is a factual dispute for trial, often with close-up photos and expert testimony about readability.
The gun predates serial-number duties. The guideline commentary expressly sets aside firearms made before the Gun Control Act of 1968 took effect, because no serial number was required then. A genuinely antique firearm presents a different case from a modern pistol with a fresh grind mark, though age must be proved, not assumed.
You did not possess the gun. Possession means control, and control is often disputed in cars with several passengers, shared homes, and guns found near but not on a person. If the gun was someone else's and you never held or controlled it, the first element fails. Fingerprint, DNA, and statement evidence usually decide this fight.
The commerce link is unproved. The government must show the gun moved in interstate or foreign commerce at some point. With most guns this proof is routine, through maker location and travel history, but routine is not automatic, and counsel tests whether the proof actually covers your gun.
The conduct fits a different charge or none at all. Where the real dispute is whether the gun was stolen rather than defaced, or where damage is cosmetic, counsel may argue the facts fit the neighboring provision better, or neither. Charging decisions are negotiable before trial, and the distinction between the 5-year and 10-year provisions gives both sides reason to examine exactly what the evidence shows about the number and the gun's history.
If you are facing this charge
Do not try to fix the number. Any grinding, restamping, or chemical restoration after the fact creates new evidence and can support new charges. Leave the gun exactly as it is and tell your lawyer where it is.
Preserve the story of how the gun came to you. Receipts, messages with the seller, pawn tickets, and the names of witnesses who saw the gun before you received it all bear on knowledge. Write down what you remember now, before memory fades, and share it with counsel rather than with agents or the seller.
Get advice before answering questions. Federal gun cases are often built from statements the accused made early, trying to explain. You have the right to speak with a lawyer first. If agents have already contacted you, read the firearms hub and the sentencing page linked above so you understand the process, then speak with counsel promptly. Early decisions shape what defenses remain open, and the facts of your case change everything.