California Penal Code 23920 makes it a misdemeanor to buy, receive, sell, offer for sale, or possess a firearm whose identification marks have been altered or removed, and, since January 1, 2024, to knowingly possess any firearm that never had a valid serial number at all. A conviction under either part carries up to six months in county jail, a fine of up to $1,000, or both.1California Legislative Information. California Penal Code 19
The Two Halves of the Statute
Subsection (a) is the older provision. It applies to anyone who buys, receives, sells, offers for sale, or possesses a firearm whose identification marks have been tampered with. The gun does not have to actually change hands. Offering it for sale is enough, and possession reaches both the firearm on your person and a firearm in a space you control, like a nightstand, a vehicle console, or a storage unit.
Subsection (b) took effect January 1, 2024. It separately criminalizes knowingly possessing any firearm that lacks a valid state or federal serial number. The target is unserialized homemade firearms and so-called ghost guns, built from parts kits, 3D-printed components, or unfinished receivers that never passed through a licensed manufacturer. The penalty is identical to subsection (a), but the available exceptions are broader.
Which Markings Count
The statute protects the manufacturer’s name, the model designation, the manufacturer’s serial number on the frame or receiver, and any distinguishing number assigned by the California Department of Justice. That last category matters for homemade firearms: California requires owners to apply to the DOJ for a unique number, and the DOJ-assigned number carries the same legal protection as a factory stamp.
Any tampering that makes those marks illegible qualifies. Grinding down a serial number, scratching digits to alter them, or cutting away the portion of metal that carries the markings all cross the line. Even partial obscuring of a single character can be enough.
What the Prosecution Has to Prove About Your State of Mind
Both subsections turn on knowledge. Under subsection (a), prosecutors must prove you knew the identification marks had been tampered with when you possessed, bought, or sold the firearm. Under subsection (b), they must prove you knew the firearm lacked a valid serial number.
That knowledge requirement is the most common defense. Inherited collections, flea-market purchases, firearms found in a storage unit you bought at auction — none of these put you on notice automatically. The problem comes when the tampering is obvious. Courts look at the totality of the circumstances: statements you made, how you acquired the gun, what you paid, and whether the defacement was visible to the naked eye. Claiming ignorance of a serial number ground flat to bare metal is a hard sell.
Penalties and Collateral Consequences
A violation of either subsection is a straight misdemeanor. Because PC 23920 does not prescribe its own punishment, the default misdemeanor penalties under Penal Code 19 apply: up to six months in county jail, a fine of up to $1,000, or both.1California Legislative Information. California Penal Code 19 Judges can grant misdemeanor probation and substitute community service or conduct restrictions for jail.
The longer-term consequence is often worse than the sentence. California imposes a 10-year ban on firearm ownership for people convicted of certain firearm-related misdemeanors.2California Department of Justice. Firearms Prohibited Categories Whether a PC 23920 conviction triggers that prohibition depends on whether the offense is included in the enumerated list under Penal Code 29805. If it applies, you lose the legal ability to buy or possess any firearm in California for a decade.
Who Is Exempt
Penal Code 23925 carves out exceptions so the statute does not trap people performing legitimate duties or trying to turn a problem firearm in.3California Legislative Information. California Penal Code 23925 – Firearms Exceptions covering both subsections include:
- Members of state or federal military forces, while on duty and within the scope of their employment.
- Peace officers, while on duty and within the scope of their employment.
- Forensic crime lab employees handling evidence firearms, while on duty.
- A person not otherwise prohibited from owning firearms who possesses the gun only long enough to deliver it to law enforcement, after notifying the agency in advance and transporting it in a locked container.
Subsection (b), the unserialized-firearm provision, adds further exceptions:
- Non-handgun firearms made or assembled before December 16, 1968.
- Firearms classified as curios, relics, or antiques under federal regulations.
- Federally licensed manufacturers, importers, and other licensees authorized to serialize firearms.
- People who applied to the DOJ for a unique serial number before January 1, 2024, and comply with all requirements, including engraving the assigned number within 10 days of receiving it.
- New California residents who apply to the DOJ for a serial number within 60 days of arrival and then complete serialization.
Federal Exposure Under 18 U.S.C. 922(k)
A defaced-serial-number case is not just a state matter. Federal law makes it a crime to possess or receive any firearm with a removed, obliterated, or altered serial number if the firearm has ever been shipped or transported across state lines.4Office of the Law Revision Counsel. 18 USC 922 – Unlawful Acts Nearly every commercially manufactured firearm crosses state lines between factory and retail, so that element is almost always satisfied.
A federal conviction carries up to five years in prison.5Office of the Law Revision Counsel. 18 USC 924 – Penalties Federal sentencing guidelines also add a four-level offense increase when a firearm in the case has an altered or obliterated serial number, which raises the recommended range considerably.6United States Sentencing Commission. Amendment 819 – USSC Guidelines The same firearm can produce a California misdemeanor and a federal felony. Federal prosecutors most often pick up these cases alongside other charges such as drug trafficking or felon-in-possession, but they can bring the serial number offense on its own.
If You Find Yourself Holding One
People end up in possession of defaced or unmarked firearms through inheritances, private used sales, and property purchases. The knowledge requirement protects you at the moment of discovery. What you do after that is what matters.
The surrender exception in Penal Code 23925 lets you keep the firearm long enough to deliver it to a law enforcement agency, as long as you notify the agency ahead of time and transport the gun in a locked container.3California Legislative Information. California Penal Code 23925 – Firearms Leaving it in a closet after you have noticed the problem is where the knowledge element engages and the safe harbor runs out. Call your local law enforcement agency, say you want to surrender the firearm, and follow their instructions for bringing it in.