A federal judge on Friday struck down California's three-decade-old ban on so-called "assault weapons", declaring the law unconstitutional in a ruling hailed by gun rights activists.

U.S. District Judge Roger Benitez of the Southern District of California said the state's assault weapons ban unlawfully deprives law-abiding Californians of the right to own firearms that are commonly owned in other states and do not fall under the Supreme Court's definition of a weapon that is not protected by the Second Amendment.

"Like the Swiss Army Knife, the popular AR-15 rifle is a perfect combination of home defense weapon and homeland defense equipment. Good for both home and battle, the AR-15 is the kind of versatile gun that lies at the intersection of the kinds of firearms protected under District of Columbia v. Heller," Benitez wrote in his opinion. " Yet, the State of California makes it a crime to have an AR15 type rifle. Therefore, this Court declares the California statutes to be unconstitutional."

He called the California law a "failed experiment" to prevent mass shootings or attacks on law enforcement. "Under no level of heightened scrutiny can the law survive," Benitez declared. The judge issued a permanent injunction against enforcement of the ban but stayed his order for 30 days to give state Attorney General Rob Bonta time to appeal the court's decision.

"This case is not about extraordinary weapons lying at the outer limits of Second Amendment protection. The banned 'assault weapons' are not bazookas, howitzers, or machine guns. Those arms are dangerous and solely useful for military purposes," Benitez said. "Instead, the firearms deemed 'assault weapons' are fairly ordinary, popular, modern rifles. This is an average case about average guns used in average ways for average purposes."

California was the first state in the nation to ban the sale of "military-style assault weapons" in 1989. State law defined an "assault weapon" as one of three types of firearms. The first is a semiautomatic centerfire rifle that does not have a fixed magazine but has one of the following features: a pistol grip that protrudes "conspicuously" beneath the action of the rifle, a thumbhole stock, a folding or telescoping stock, a grenade or flare launcher, a flash suppressor, or a forward pistol grip. The second type is a semiautomatic centerfire rifle that has a fixed magazine that can hold 10 or more rounds. The third type of banned firearm is a semiautomatic centerfire rifle that has an overall length of less than 30 inches.

In 2019, California resident James Miller and several state gun rights groups including the San Diego County Gun Owners Political Action Committee, California Gun Rights Foundation, Second Amendment Foundation, and Firearms Policy Coalition challenged the law in court. Plaintiffs argued that gun owners who wanted to use high-capacity magazines in their legal semiautomatic rifles or pistols were prohibited from doing so by the California law, which would impose criminal penalties on otherwise law-abiding citizens for modifying their firearms.

The lawsuit said California is "one of only a small handful states to ban many of the most popular semiautomatic firearms in the nation because they possess one or more common characteristics, such as pistol grips and threaded barrels."

The state argued that firearms classified as assault weapons under the law were more dangerous and were used in more crimes and mass shootings.

Benitez observed that facts don't support the state's assertions and that the law has not demonstrably prevented mass shootings.

"One is to be forgiven if one is persuaded by news media and others that the nation is awash with murderous AR-15 assault rifles," he said. "The facts, however, do not support this hyperbole, and facts matter."

Benitez also ridiculed the term "assault weapon", calling it a "misnomer."

"These prohibited guns, like all guns, are dangerous weapons. However, these prohibited guns, like all guns, can be used for ill or for good. They could just as well be called 'home defense rifles' or 'anti-crime guns,'" said the judge.

Reacting to the decision, California Gov. Gavin Newsom (D) slammed the court's opinion.

"Today's decision is a direct threat to public safety and the lives of innocent Californians, period," he said in a statement. "As the son of a judge, I grew up with deep respect for the judicial process and the importance of a judge's ability to make impartial fact-based rulings, but the fact that this judge compared the AR-15 – a weapon of war that's used on the battlefield – to a Swiss Army Knife completely undermines the credibility of this decision and is a slap in the face to the families who've lost loved ones to this weapon. We're not backing down from this fight, and we'll continue pushing for common sense gun laws that will save lives."

But gun rights groups praised the ruling.

"In his order today, Judge Benitez held what millions of Americans already know to be true: Bans on so-called 'assault weapons' are unconstitutional and cannot stand," said Firearms Policy Coalition president Brandon Combs. "This historic victory for individual liberty is just the beginning, and FPC will continue to aggressively challenge these laws throughout the United States. We look forward to continuing this challenge at the Ninth Circuit and, should it be necessary, the Supreme Court."