Duncan v. Bonta is a federal lawsuit challenging California’s ban on ammunition magazines that hold more than 10 rounds, brought by gun owners and the California Rifle & Pistol Association against California Attorney General Rob Bonta. After nearly a decade of trial and appellate rulings going in opposite directions, the case is now at the U.S. Supreme Court, which distributed the plaintiffs’ petition for certiorari for its conference of March 27, 2026.1Supreme Court of the United States. Docket for Case 25-198 Whether the justices agree to hear it will likely determine whether states can prohibit possession of what the firearms industry calls standard-capacity magazines.
The Law Being Challenged
California Penal Code Section 32310 prohibits manufacturing, importing, selling, giving, lending, buying, receiving, or possessing any large-capacity magazine in the state.2California Legislative Information. California Penal Code 32310 A companion statute, Section 16740, defines a large-capacity magazine as any ammunition feeding device that accepts more than 10 rounds, with narrow carve-outs for permanently modified devices, .22 caliber tube-style feeders, and tubular magazines in lever-action firearms.3California Legislative Information. California Penal Code 16740
The ban reaches magazines regardless of when they were bought. Anyone who possessed one before the possession prohibition took effect on July 1, 2017, was required to remove it from California, sell it to a licensed dealer, or surrender it to law enforcement for destruction. The state offered no compensation for surrendered property.2California Legislative Information. California Penal Code 32310 That disposal-without-compensation feature is what gives the plaintiffs their second constitutional claim.
What Each Side Is Arguing
The plaintiffs press two constitutional theories.
Second Amendment
The Second Amendment claim runs through the framework the Supreme Court established in New York State Rifle & Pistol Association, Inc. v. Bruen in 2022. Bruen replaced the interest-balancing tests most lower courts had used with a two-step inquiry: first, whether the Second Amendment’s plain text covers the conduct at issue, and second, whether the challenged regulation is consistent with the nation’s historical tradition of firearm regulation.4Supreme Court of the United States. New York State Rifle and Pistol Association Inc. v. Bruen
The plaintiffs argue that magazines are essential components that make firearms functional, placing them within the text’s protection of the right to “keep and bear arms.” California responds that a firearm operates with a 10-round magazine, which makes higher-capacity versions accessories rather than protected arms. On history, the state points to old restrictions on especially dangerous weapons and on the storage of large quantities of gunpowder as analogous precedents; the plaintiffs say none of those resemble a ban on commonly owned firearm parts.
Takings Clause
The second claim invokes the Fifth Amendment. The plaintiffs argue that forcing owners of lawfully acquired magazines to modify, sell, move, or surrender them, with no compensation, is an unconstitutional taking of private property.5Supreme Court of the United States. Petition for Writ of Certiorari, Duncan v. Bonta, No. 25-198 The Takings issue gives the Supreme Court a second, independent reason to grant review.
The Ninth Circuit’s 2025 Ruling
On March 20, 2025, the Ninth Circuit, sitting en banc for the second time in the case’s history, upheld the California ban.6United States Court of Appeals for the Ninth Circuit. Duncan v. Bonta (2025) The majority rested its decision on two independent grounds, either of which it said would sustain the statute.
First, large-capacity magazines are not “arms” within the Second Amendment’s text. The court treated them as optional accessories rather than necessary components. Second, even if the text did cover them, the ban fits within a historical tradition of regulating dangerous weapon components and prohibiting especially dangerous uses of weapons.6United States Court of Appeals for the Ninth Circuit. Duncan v. Bonta (2025)
The dissenting judges pushed back on both points. Judge Bumatay wrote that the majority had returned to the interest balancing Bruen expressly rejected, dressing policy preferences as constitutional analysis. Judge VanDyke called the distinction between an “arm” and an “accessory” unworkable, arguing that magazines holding more than 10 rounds come standard with many of the most popular firearms sold nationwide, which makes them among the most commonly owned items in the country. On history, the dissenters said California had identified no early law that actually resembled a ban on commonly owned firearm parts; gunpowder-storage rules and public-carry restrictions, they wrote, addressed different problems in different ways. Judge R. Nelson also questioned whether the en banc court had statutory jurisdiction to decide the case as it did.6United States Court of Appeals for the Ninth Circuit. Duncan v. Bonta (2025)
How the Case Reached This Point
The case has been litigated since 2017 under Judge Roger Benitez in the Southern District of California, who twice struck the ban down. The Ninth Circuit reversed him in 2021 en banc. The Supreme Court then decided Bruen in 2022, vacated that Ninth Circuit ruling, and sent Duncan back for reconsideration. On remand, Judge Benitez again enjoined the law in 2023. The Ninth Circuit’s March 2025 en banc reversal is the ruling now under review.7United States Court of Appeals for the Ninth Circuit. Duncan v. Bonta (2021)
One episode in that timeline matters for current magazine owners. Between March 29 and April 5, 2019, a district-court injunction briefly blocked the entire statute, and many Californians bought magazines during what gun owners call “Freedom Week.” Those purchases were lawful when made, and enforcement against Freedom Week buyers has been complicated by the injunctions that have come and gone since. Owners with proof of purchase date stand on firmer legal ground than those without.
Where the Case Stands Now
The plaintiffs filed their petition for a writ of certiorari on August 15, 2025, docketed as No. 25-198. The Court distributed it for the conference of March 27, 2026, when the justices will privately vote on whether to take the case.1Supreme Court of the United States. Docket for Case 25-198 A grant would send the case into full briefing and oral argument, most likely in the Court’s next term, with a decision to follow. A denial would leave the Ninth Circuit’s ruling in place and the California ban intact.
In the meantime, the ban on manufacturing, importing, and selling large-capacity magazines has been enforced consistently throughout the litigation. The possession prohibition has moved in and out of effect as different injunctions have taken hold and been stayed. Californians who own pre-ban or Freedom Week magazines should watch for any order the Supreme Court issues, because the enforceability of the possession piece can change on short notice.
Why the Ruling Would Reach Beyond California
Fourteen states and the District of Columbia restrict magazine capacity in some form, with limits that vary from 10 to 17 rounds. A Supreme Court decision on the merits in Duncan could validate or invalidate all of those laws at once.
The case also tests how strictly lower courts have to apply Bruen. The Ninth Circuit dissenters accused the majority of performing the text-and-history analysis in name while doing policy balancing in fact. If the Supreme Court sees it the same way, a Duncan ruling could tighten the rules for every kind of firearm regulation, not just magazine limits. That is why the case is being watched as potentially the most consequential Second Amendment decision since Bruen itself.