District court

On August 15, 2019, James Miller, a board member of the San Diego County Gun Owners, sued Attorney General Xavier Becerra and the Director of the California Bureau of Firearms,^[8][16] alleging that the ban was an unconstitutional restriction of Second Amendment rights. He was joined by the San Diego County Gun Owners Political Action Committee, California Gun Rights Foundation, Second Amendment Foundation, and Firearms Policy Coalition, along with three other San Diego County residents who said they legally own rifles or pistols but are unable to use high-capacity magazines in them due to the law.^[4][7][17]

The case was argued before Senior Judge Roger Benitez of the U.S. District Court for the Southern District of California. The plaintiffs argued that the definition of "assault weapon" is politically motivated and prevents law-abiding citizens from obtaining and using firearms for self-defense, hunting, and other legal purposes.^[8] Becerra's office argued that the ban was necessary because assault weapons are more lethal and are disproportionately used in crimes and mass shootings.^[4] Benitez denied requests by Everytown for Gun Safety and the Giffords Law Center to Prevent Gun Violence to file amicus briefs in favor of the state.^[12] In April 2021, Rob Bonta took over the defense when he succeeded Becerra as Attorney General of California.

On June 4, 2021, Benitez ruled in favor of the plaintiffs, declaring the AWCA to be unconstitutional and issuing a permanent injunction against enforcing specific provisions of the law.^[10] He opened the 94-page ruling by likening an AR-15 style rifle to a Swiss Army knife as "a perfect combination of home defense weapon and homeland defense equipment" and describing the AR-15 as "good for both home and battle", citing District of Columbia v. Heller and United States v. Miller.^{[4][18][19][20][21]} He described the ban as a failed experiment and reasoned that the ban covers weapons that are commonly used for legal purposes. In dismissing the need for a ban on assault rifles, he cited the prevalence of stabbing deaths in the state compared to murders by rifle, and also claimed that "More people have died from the COVID-19 vaccine than mass shootings in California."^{[4][13][22][23]} Upon Bonta's request, Benitez granted a stay of the injunction for 30 days pending appeal.^[4]

Appellate court

On June 10, 2021, California Attorney General Bonta and Bureau of Firearms Director Luis Lopez appealed the ruling to the Ninth Circuit Court of Appeals.^[10][16] On June 21, a three-judge panel of the Ninth Circuit – Barry G. Silverman, Jacqueline Nguyen, and Ryan D. Nelson – granted their request to extend the stay as appeals are litigated.^[1][2] Mayor Sam Liccardo of San Jose has invited other California cities to join an amicus brief supporting the state's appeal.^[24][25]

Another challenge to the AWCA, Rupp v. Bonta, has already been appealed to the Ninth Circuit court from the U.S. District Court for the Central District of California.^[26]

On November 30, 2021, the Ninth Circuit Court restored the state ban on high-capacity magazines in Duncan v. Bonta, suggesting that the court would also reverse the lower court ruling in Miller v. Bonta.^[15]

On June 23, 2022, the U.S. Supreme Court decided New York State Rifle & Pistol Association, Inc. v. Bruen, broadly rejecting any "means-end tests" such as the strict or intermediate scrutiny the Ninth Circuit had applied in upholding the constitutionality of various gun regulations. The opinion, written by Justice Clarence Thomas, emphasized that going forward the standard for applying the Second Amendment will require the government to "justify its regulation by demonstrating that it is consistent with the Nation’s historical tradition of firearm regulation." This newly clarified "text as informed by history" standard is widely expected to significantly affect how gun control cases such as Miller and Rupp are decided.^[27]

On August 1, 2022, the Ninth Circuit three-judge panel vacated and remanded the case “for further proceedings consistent with the United States Supreme Court’s decision in New York State Rifle & Pistol Ass’n, Inc. v. Bruen.”

Remanded case at District Court

On October 19, 2023 Judge Roger Benitez delivered a decision on the remanded case in the United States District Court Southern District of California. In this decision he ruled the California assault weapons ban unconstitutional for the second time in that it violated the defendants' Second Amendment rights and granted a permanent injunction on the enforcement of the California statute. A 10 day stay on this ruling was also issued by Judge Benitez in anticipation of an appeal to the Ninth Circuit.^[28]