California signs law requiring 3D printers to block firearm printing

The new law regulates the sale and transfer of 3D printers, not their ownership or use, and does not require existing printers to be retrofitted with blocking technology. Manufacturers will only be required to include firearm-blocking features once ASTM International, a non-profit organisation that sets voluntary standards across industries, publishes or adopts a standard for such technology.

The California Department of Justice is mandated to check for a standard quarterly, starting no later than July 1, 2027, and continuing until July 1, 2029. If no standard has been published by that date, the DOJ is no longer required to check, meaning the process to write the guidelines or regulations that manufacturers need to follow to sell 3D printers in California may not even begin.

Two primary methods exist for detecting whether a print file is intended for a firearm: matching against a known database of gun files, or analysis by a trained model to determine whether a design could be used as a firearm. Both techniques have shortcomings. The database approach could be defeated by modifying the file, such as changing its size or splitting it into multiple pieces for later assembly. The model-based approach is prone to false positives and could prevent the printing of barrels, brackets, levers, tubes, and other parts that may look similar but have legitimate uses.

The Electronic Frontier Foundation said in June 2026 that "there is no world where the mandated technology actually works as intended." The California law attempts to address these concerns by mandating the DOJ to base its implementation on standards set by ASTM International rather than defining the technology itself.

Analysis

Why This Matters

The law could set a precedent for other states and affect the entire US 3D printer market, as California is a large consumer market that often drives national manufacturing standards.
The effectiveness of the law depends entirely on whether ASTM International can develop a workable blocking standard, a process the Electronic Frontier Foundation has described as unworkable.
3D printer buyers and hobbyists face no immediate change, but future purchases may include technology that could restrict legitimate printing if detection systems produce false positives.

Background

California is the second US state after New York to pass laws requiring firearm-blocking technology on 3D printers. Similar bills are moving through legislatures in Colorado and Washington state. The laws respond to concerns about the proliferation of 3D-printed firearms, including so-called "ghost guns" that lack serial numbers and can be made without background checks. The technology to block firearm printing remains controversial and largely untested at scale.

Key Perspectives

California lawmakers and gun control advocates: The law aims to reduce the availability of untraceable 3D-printed firearms without banning 3D printing itself, working within a market-based framework that defers technical decisions to standards bodies. 3D printing community and the Electronic Frontier Foundation: Critics argue the mandated blocking technology does not exist in a reliable form and will either be easily bypassed or block legitimate prints through false positives, effectively imposing surveillance on all users. ASTM International: The non-profit standards organisation now faces pressure to produce a workable standard within a defined timeframe, or the law's core requirement may lapse entirely.

What to Watch

Whether ASTM International publishes a firearm-blocking standard by July 2027, and what form that standard takes.
Whether other states adopt similar laws and whether they create a patchwork of differing requirements for manufacturers.
Legal challenges once the DOJ attempts to implement any standard that emerges.

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