WASHINGTON, D.C. A 27-state coalition led by Montana Attorney General Austin Knudsen and Idaho Attorney General Ral Labrador is asking the U.S. Supreme Court to hear Duncan v. Bonta, a challenge to Californias prohibition on magazines holding more than ten rounds. In an amicus brief filed September 18, 2025, the states urge the Court to grant certiorari and reverse a March 20, 2025 ruling by the U.S. Court of Appeals for the Ninth Circuit that upheld the California law. The filing frames magazines that exceed ten roundsdescribed as plus-ten magazinesas protected by the Second Amendment because they are essential components of modern arms, and it contends Californias restriction conflicts with Supreme Court precedent. The brief characterizes the Ninth Circuits decision as an obvious error on a core issue of constitutional law that warrants correction by the high court. According to the coalition, the ban burdens the rights of law-abiding citizens and cannot be squared with contemporary Second Amendment jurisprudence. The states position their involvement as a defense of citizens rights against unnecessary intrusions, specifically focusing on possession and use of higher-capacity magazines that they describe as common in lawful use. Signatories span much of the country: Montana, Idaho, Alabama, Alaska, Arkansas, Florida, Georgia, Iowa, Indiana, Kansas, Kentucky, Louisiana, Mississippi, Missouri, Nebraska, New Hampshire, North Dakota, Ohio, Oklahoma, South Carolina, South Dakota, Tennessee, Texas, Utah, West Virginia, and Wyoming, along with the Arizona Legislature. By highlighting the breadth of participation, the filing argues that the question presented is national in scope and not confined to a single states policy choice. Beyond Californias statute, the coalition points to a pattern in jurisdictions that also restrict popular semiautomatic rifles such as the AR-15. The brief describes the combination of rifle restrictions and magazine-capacity caps as a double whammy to constitutional rights and asserts that legislative and judicial approaches in those jurisdictions conflict with Supreme Court precedent. That asserted conflict forms a central argument for review: the coalition says the justices should resolve inconsistency among lower courts and clarify whether commonly used magazines fall within the Second Amendments protections. Knudsen underscores the stakes by arguing that the Ninth Circuits ruling deprives citizens of fundamental rights, their property, and their ability to defend themselves, and that Supreme Court intervention is required to correct recurring misapplications of the law. The brief further asserts that constitutional rights do not stop at state lines, casting Duncan as a vehicle to address national questions about limits on magazine capacity. The activity is not limited to California. A week earlier, the same multistate group filed an amicus brief supporting Gators Custom Guns, Inc. in litigation over Washington states large-capacity magazine law. In that matter, the Washington ban was first struck down by a lower court before being upheld by the Washington Supreme Court; petitioners have now asked the U.S. Supreme Court to review that outcome as well. The coalition cites the Washington case to illustrate the spread of capacity limits and, in its view, the need for definitive guidance from the nations highest court. If the Court grants review in Duncan, the legality of plus-ten magazine restrictions would be squarely before the justices, with potential implications for states that maintain similar limits. For the 27 jurisdictions aligned with Knudsen and Labrador, the case represents an opportunity to confirm whether commonly used magazines are protected as components of modern firearms and to address what the coalition describes as divergent approaches among appellate courts.