Possession of a Firearm Without a Serial Number: CA Penal Code

In California, possession of a firearm without a serial number is a misdemeanor as of January 1, 2024. Under Penal Code Section 23920, anyone who knowingly possesses a firearm that lacks a valid state or federal serial number can be sentenced to up to one year in county jail if the weapon is a handgun, or up to six months for a rifle or shotgun, along with a fine of up to $1,000. Each unserialized firearm is charged as a separate offense, and the criminal case is only part of the exposure: a civil statute lets private plaintiffs sue for at least $10,000 per weapon.

What Counts as an Unserialized Firearm

The ban reaches any firearm without a serial number imprinted by a federally licensed manufacturer or issued by the California Department of Justice. It does not matter how the gun came to exist. A weapon assembled from a parts kit, 3D-printed, milled from an unfinished frame, or handed down through a family all fall under the same rule if no valid serial number is on the frame or receiver.¹

Before AB 1621 took full effect on January 1, 2024, the original serialization law (AB 857, effective 2018) only reached people who were actively building firearms. Simple possession of an already-unserialized gun was not itself a crime. That gap is now closed.¹

The word “knowingly” is doing real work in the statute. The prosecution must show the person knew they possessed a firearm that lacked a valid serial number. Someone who inherits a gun and has no reason to know it is unserialized has a factual defense against the possession charge, though whether it succeeds depends on the specifics.¹

Criminal Penalties by Firearm Type

The maximum sentence turns on what kind of firearm is involved:

Handguns: up to one year in county jail, a fine of up to $1,000, or both.
Rifles, shotguns, and other long guns: 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 the same closet produce three charges, not one.²

The statute also contains a greater-penalty clause: a conviction under Section 29180 does not preclude prosecution under any other law carrying a heavier sentence. Someone who is already a prohibited person, whether because of a prior felony conviction, an active restraining order, or another disqualifier, can face felony weapons charges layered on top of the ghost gun misdemeanor. If the firearm surfaces during a violent crime investigation, additional charges are the norm rather than the exception.²

Law enforcement can seize any unserialized firearm found during an investigation or arrest. Unfinished frames and receivers that qualify as firearm precursor parts are classified as a nuisance under California law and are subject to confiscation and destruction.¹

Firearms That Are Exempt

Not every gun without a visible serial number is illegal. Penal Code Section 29181 sets out specific exempt categories:

Non-handgun firearms 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 invoke the antique and curio exemption, but the qualifying criteria are narrow. The firearm has to meet the federal regulatory definition, which generally covers weapons manufactured before 1899 or certain firearms the ATF has certified as collectible. Age alone is not enough.

How to Bring an Unserialized Firearm Into Compliance

If a firearm is not exempt and does not carry a valid serial number, California requires the possessor, as a builder, to obtain a unique serial number from the Department of Justice and engrave it on the weapon. Applications go through the California Firearms Application Reporting System (CFARS). The initial fee is $46.19, which covers the firearms eligibility background check and one serial number, with each additional serial number costing $15.⁴

The DOJ has 90 calendar days to approve or deny the application. Once approved, the number must be engraved on the frame or receiver within 10 days, at least .003 inches deep and in characters no smaller than 1/16 of an inch, placed conspicuously and in a way that cannot easily be removed or covered. The engraving must also include the model designation if one exists, the builder’s name as registered with the DOJ, the caliber or gauge, and the city and state where the firearm was made.⁵

Polymer firearms have an additional requirement. 3.7 ounces of type 17-4 PH stainless steel must be embedded in the plastic during fabrication, and the serial number engraved on that insert, so the marking cannot be melted or dissolved off.² After engraving, the builder uploads images through CFARS to close out the process.⁴

One boundary worth flagging: a non-federally-licensed person who builds a firearm cannot sell or transfer it, with a narrow exception for surrendering it to law enforcement. Compliance produces a legally possessed firearm for personal use, not one that can be handed off to a friend or family member.²

Civil Liability on Top of Criminal Charges

Senate Bill 1327 created a separate private right of action. Any person in California can sue someone who manufactures, distributes, imports, or sells an unserialized firearm in the state. If the plaintiff wins, the court must award at least $10,000 in statutory damages per weapon or precursor part, plus injunctive relief and attorney’s fees. The claim reaches anyone who aids or abets the prohibited conduct, and the statute of limitations runs four years from when the cause of action accrues.⁶

A misdemeanor conviction and a civil judgment are independent. Someone acquitted of the criminal charge can still be sued, and vice versa.

The Ban on Selling or Transferring

AB 1621 also made it illegal for anyone to sell or transfer a firearm that lacks a serial number imprinted by a federally licensed manufacturer. The same law reclassified unfinished frames and receivers that can readily be completed into functional firearms as “firearm precursor parts,” which cannot be sold outside regulated channels. Buying an “80% lower receiver” kit online and having it shipped to a California address is no longer legal unless the transaction goes through a licensed vendor who runs a background check.¹

Defenses to a Possession Charge

Because Section 23920 requires knowing possession, a defense often starts with what the person actually knew about the firearm. Genuine ignorance that a weapon lacked a valid serial number can defeat the mental-state element.¹

Standard procedural defenses also apply. If the firearm was found during an unlawful search or seizure, the evidence may be suppressed. Second Amendment challenges have been raised against California’s ghost gun laws, though courts have generally upheld the regulations to date. Whether any defense actually works turns on the facts, and anyone facing charges should speak with a criminal defense attorney rather than rely on general information.

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 Department of Justice. Unique Serial Number Application
5
Legal Information Institute. Cal. Code Regs. Tit. 11, 5520
6
California Legislative Information. SB 1327