Yes. Ghost guns are illegal to possess in California unless they carry a valid serial number issued by the state Department of Justice and are registered with the state. Since January 1, 2024, knowingly possessing any firearm without a state or federal serial number is a misdemeanor, and manufacturing, selling, or transferring unserialized firearms triggers additional criminal penalties and civil liability.1California Department of Justice. Unique Serial Number Application
What California Treats as a Ghost Gun
A ghost gun, in practical terms, is any firearm or firearm component that lacks a valid serial number. That includes completed firearms built from kits, 3D-printed guns, and frames or receivers machined from partially completed blanks sometimes marketed as “80% lowers.”
California’s firearm definition is broader than most people expect. It covers any device designed to expel a projectile through a barrel by force of an explosion or other combustion.2California Legislative Information. California Penal Code 16520 For the ghost gun rules, it also reaches frames, receivers, and “firearm precursor parts,” which are partially completed components that can be readily finished into a functioning frame or receiver.3California Legislative Information. AB-1621 Firearms: Unserialized Firearms Product labels don’t control. If the item can be readily converted into a working firearm, the state treats it as one.
The Possession Rule and the 2024 Deadline
The core rule is simple. On or after January 1, 2024, knowingly possessing a firearm without a valid serial number is a misdemeanor.1California Department of Justice. Unique Serial Number Application Every unserialized firearm is a separate offense, so a collection of ghost guns means a stack of separate charges.
If you already owned an unserialized firearm before that date, the deadline to apply for a state-issued serial number was January 1, 2024. Miss it and the firearm is illegal to possess.
New residents get a short window. If you move to California with an unserialized firearm, you have 60 days after arriving to apply for a serial number.
How to Make a Self-Built Firearm Legal
Before manufacturing or assembling any firearm, you must apply to the California Department of Justice for a unique serial number.4California Legislative Information. California Penal Code 29180 The application asks for your full name, address, date of birth, and a description of the firearm you plan to build, and the DOJ runs a background check to confirm you’re legally eligible.1California Department of Justice. Unique Serial Number Application
Once you receive the number, you have 10 days after finishing the firearm to engrave the number and notify the DOJ.4California Legislative Information. California Penal Code 29180 From that point the firearm is treated like any commercially manufactured gun and is subject to safe storage and transfer rules.
Engraving Standards
The engraving has to be conspicuous, placed on the frame or receiver, and cut to a minimum depth of .003 inches with characters no smaller than 1/16 of an inch. Depth is measured from the flat metal surface, not from the peaks of the engraving.5Legal Information Institute. Cal. Code Regs. Tit. 11, 5520 – Procedures to Engrave or Permanently Affix a Serial Number
Polymer firearms carry an extra requirement. You must embed at least 3.7 ounces of type 17-4 PH stainless steel within the plastic frame or receiver, and the serial number must be engraved on that steel insert.4California Legislative Information. California Penal Code 29180 For 3D-printed firearms, the stainless steel requirement is non-negotiable.
What You Still Can’t Do, Even With a Serial Number
A DOJ serial number lets you keep a self-built firearm. It does not unlock every activity.
You Cannot Sell or Transfer a Self-Made Firearm
California prohibits the sale or transfer of any firearm that doesn’t carry a serial number placed by a federally licensed manufacturer or importer.3California Legislative Information. AB-1621 Firearms: Unserialized Firearms A state DOJ number satisfies the possession rule but not the transfer rule. In practice, privately built firearms in California are essentially non-transferable to other individuals.
Precursor Parts
Buying, selling, or transferring firearm precursor parts is illegal in California unless those parts are regulated under federal law to the same extent as completed frames or receivers.3California Legislative Information. AB-1621 Firearms: Unserialized Firearms That effectively shuts down retail sales of unfinished “80% lower” kits.
CNC Milling at Home
Only federally licensed firearms manufacturers or importers may use a computer numerical control milling machine to make a firearm, frame, receiver, or precursor part.3California Legislative Information. AB-1621 Firearms: Unserialized Firearms The garage CNC route that was once common is off the table without a federal manufacturing license.
Criminal Penalties
Possessing an Unserialized Firearm
Knowingly possessing a firearm without a valid serial number on or after January 1, 2024, is a misdemeanor, and each firearm is a separate offense.1California Department of Justice. Unique Serial Number Application
Manufacturing Without a Serial Number
Building a firearm without first obtaining a serial number is punishable by up to one year in county jail, a fine of up to $1,000, or both for handguns. For all other firearms, the maximum jail time is six months with the same $1,000 fine cap.4California Legislative Information. California Penal Code 29180 Each firearm built in violation is a distinct offense, and prosecutors are not barred from adding charges under other statutes that carry stiffer penalties.
Prohibited Persons
Anyone barred from possessing firearms faces far worse consequences. Federal prohibited categories include anyone convicted of a crime punishable by more than one year in prison, anyone subject to a domestic violence restraining order, and anyone convicted of misdemeanor domestic violence.6Bureau of Alcohol, Tobacco, Firearms and Explosives. Identify Prohibited Persons California’s list is broader. A prohibited person caught with any firearm, serialized or not, faces up to three years in state prison.
Sentencing Enhancements
If a ghost gun is used during a felony, California’s sentencing enhancement laws can add years to a prison term. Enhancements for personal use of a firearm during a violent felony are imposed on top of the base sentence for the underlying crime, and gang-related offenses carry their own additional enhancements.
Civil Lawsuits Over Ghost Guns
Criminal charges are not the only exposure. Senate Bill 1327 created a private right of action allowing anyone to sue a person who manufactures, distributes, or sells unserialized firearms in California. Successful plaintiffs can recover at least $10,000 in statutory damages per weapon.7California Legislative Information. California Senate Bill 1327 – Firearms: Private Rights of Action The same conduct can trigger both prosecution and a civil suit.
Narrow Exemptions
A few categories fall outside the ghost gun restrictions. Federally licensed manufacturers and importers may produce unserialized components during business operations, though they must serialize any firearm before selling or transferring it. Law enforcement agencies and forensic laboratories can possess unserialized firearms for official investigations and testing.
Antique firearms are also exempt. California generally defines an antique as one manufactured before January 1, 1899, or one that uses fixed ammunition made in or before 1898 for which ammunition is no longer commercially available.8California Legislative Information. California Penal Code 16170 – Antique Firearm Collectors holding qualifying antiques for display or historical purposes don’t need to obtain serial numbers or register them.
Changes Coming January 1, 2026
Two additional laws take effect at the start of 2026. Senate Bill 704 requires firearm barrels sold separately (not already attached to a firearm) to be transferred in person through a licensed firearms dealer. Online retailers shipping barrels to California residents must send them to a licensed dealer for final transfer. A first or second violation is a misdemeanor; a third or subsequent violation can be charged as a misdemeanor or a felony.9California Department of Justice. Information Bulletin 2025-DLE-18
Assembly Bill 1263 broadens the definition of “firearm manufacturing machine” to reach any machine marketed or designed to manufacture firearm components or accessories, not just 3D printers and CNC mills. The law also creates a category called a “digital firearm manufacturing code,” covering CAD files, CAM files, and similar digital instructions that can program a machine to produce firearms, frames, receivers, precursor parts, silencers, or large-capacity magazines.9California Department of Justice. Information Bulletin 2025-DLE-18 Sharing or distributing digital blueprints for firearms manufacturing will face new legal scrutiny in California once the law takes effect.