Possession of a Firearm Without a Serial Number: Penalties and Defenses

In California, possession of a firearm without a serial number is a misdemeanor under Penal Code Section 23920. Since January 1, 2024, anyone who knowingly keeps a gun that lacks a valid state or federal serial number can be charged, and the penalties scale with the type of firearm: up to one year in county jail for a handgun and up to six months for a rifle or shotgun, plus a fine of up to $1,000 in either case. Each unserialized firearm is a separate count.

What the Possession Ban Covers

The possession offense was added by Assembly Bill 1621 and took full effect at the start of 2024. Before that, California’s serialization law reached only people who were actively building or assembling a firearm. Now, the gun itself is the problem: if it does not carry a serial number imprinted by a federally licensed manufacturer or a number issued by the California Department of Justice, keeping it is a crime.¹

The statute uses the word “knowingly.” The prosecution has to show the person was aware they had a firearm that lacked a valid serial number. That mental-state requirement matters when the gun was inherited, borrowed, or acquired in circumstances where the owner had no realistic way to know its status.¹

The ban reaches homemade guns built from parts kits, 3D-printed firearms, machined builds, and any commercially made firearm whose serial number has been removed or defaced. Law enforcement is authorized to seize unserialized firearms found during investigations or arrests.¹

Penalties by Firearm Type

The sentencing exposure under Penal Code Section 29180 breaks down by category:

Handguns: up to one year in county jail, a fine of up to $1,000, or both.
All other firearms, including rifles and shotguns: up to six months in county jail, a fine of up to $1,000, or both.

Each unserialized firearm counts as a separate offense. Three unserialized handguns in a safe can produce three charges, not one.²

Section 29180 also includes a catch-all: a conviction under the serialization statute does not block prosecution under any other law carrying a greater penalty. Someone already prohibited from owning firearms, whether from a prior felony conviction, a restraining order, or another disqualifier, can face felony weapons charges stacked on top of the ghost gun misdemeanor. The same is true when an unserialized firearm turns up during a violent crime investigation.²

Sales, Transfers, and Precursor Parts

Possession is only one piece of what AB 1621 changed. Selling or transferring a firearm that lacks a federal-manufacturer serial number is prohibited. A non-federally-licensed person who builds a firearm cannot transfer it at all, with a narrow exception for surrendering it to law enforcement. Homemade firearms are strictly for the builder’s personal use.²

The law also regulates “firearm precursor parts,” meaning unfinished frames or receivers that have reached a point where they can readily be completed into a working firearm. Buying an “80% lower receiver” kit online and having it shipped into California is no longer legal unless the sale goes through a licensed vendor who runs a background check. Unlawfully possessed precursor parts are classified as a nuisance and subject to confiscation and destruction.¹

Firearms That Are Exempt

Not every gun without a visible serial number is contraband. Penal Code Section 29181 lists specific categories that fall outside the serialization requirement:

Long guns made or assembled before December 16, 1968.
Firearms that qualify as antiques or as curios and relics under the federal definition in 27 CFR Section 479.11.
Firearms that already carry a valid state or federal serial number.
Firearms entered into California’s centralized registry before July 1, 2018 with a distinguishing number.
Firearms with serial numbers assigned under Chapter 53 of Title 26 of the United States Code (the National Firearms Act registry).

Collectors most often point to the antique and curio exemption, but a firearm has to meet the federal definition. That generally means weapons made before 1899 or specific guns the ATF has certified as collectible. Age alone is not enough.

Civil Liability on Top of Criminal Charges

Senate Bill 1327 created a private right of action. Any person in California can sue someone who manufactures, distributes, imports, or sells an unserialized firearm in the state. A successful plaintiff must be awarded at least $10,000 in statutory damages per weapon or precursor part, along with injunctive relief and attorney’s fees. The claim reaches anyone who aids or abets the prohibited conduct, and the statute of limitations is four years from when the cause of action accrues.⁴

The civil exposure sits alongside the criminal exposure, not in place of it. For someone who sold or distributed, the financial risk can far exceed a misdemeanor fine.

Getting Into Compliance

If you built a firearm yourself, or inherited one that has no serial number but is not exempt, the path to legal possession runs through the California Firearms Application Reporting System (CFARS). You apply to the DOJ for a unique serial number, upload a copy of your California driver license or state ID, provide a description of the firearm, and submit standard personal information.⁵

The initial fee is $46.19, which covers a firearms eligibility background check ($31.19) and one serial number ($15). Additional serial numbers in the same transaction cost $15 each. A California ID marked “FEDERAL LIMITS APPLY” requires proof of lawful presence, such as a passport or certificate of naturalization. The DOJ has 90 calendar days to approve or deny the application.⁵

Once approved, the serial number has to be engraved within 10 days of completing the firearm, and the engraving must meet state technical standards: at least .003 inches deep, characters no smaller than 1/16 of an inch, placed conspicuously on the frame or receiver so it cannot easily be removed, altered, or covered. The engraving must also include the model designation (if any), the builder’s first and last name as registered with the DOJ, the caliber or gauge, and the city and state of manufacture.⁶

Polymer firearms carry an added rule: 3.7 ounces of type 17-4 PH stainless steel must be embedded in the plastic during fabrication, and the serial number is engraved on that steel insert.² After engraving, images must be uploaded through CFARS to close out the record.

Defenses to a Possession Charge

The “knowingly” standard is the first place a defense attorney will look. If a person genuinely did not know a firearm they possessed lacked a valid serial number, that lack of knowledge can defeat the possession element. Inheritance cases and gifts from older relatives are common fact patterns.¹

An exemption under Section 29181 can also end the case. If the firearm is a qualifying antique, a curio or relic, a pre-1968 long gun, or already carries a valid serial number from another source, the possession offense does not apply.³

Standard Fourth Amendment defenses remain in play, including challenges to the search or seizure that produced the firearm. Second Amendment challenges to California’s ghost gun framework have been raised, though courts have generally upheld the regulations. Whether any of these arguments succeeds depends on the specific facts, and anyone facing charges should talk with a criminal defense attorney rather than relying on general information.

Federal Law Runs in Parallel

California’s possession ban is not the only rule in play. The ATF’s 2022 Final Rule 2021R-05F updated the federal definition of “frame or receiver” to include partially complete versions that can readily be finished, and formally defined “privately made firearm” as any firearm built outside a licensed manufacturer. In Bondi v. VanDerStok, decided in March 2025, the Supreme Court held 7–2 that the rule is not facially inconsistent with the Gun Control Act.⁷ Someone who moves unserialized firearms across state lines can also face federal charges under the trafficking and straw purchasing offenses created by the Bipartisan Safer Communities Act, independent of any California prosecution.⁸

1
California Legislative Information. AB-1621 Firearms: Unserialized Firearms
2
California Legislative Information. California Penal Code 29180
3
California Legislative Information. California Penal Code 29181
4
California Legislative Information. SB 1327
5
California Department of Justice. Unique Serial Number Application
6
Legal Information Institute. Cal. Code Regs. Tit. 11, 5520 – Procedures to Engrave or Permanently Place Unique Serial Numbers
7
Supreme Court of the United States. Bondi v. VanDerStok, No. 23-852
8
United States Department of Justice. Fact Sheet: Two Years of the Bipartisan Safer Communities Act