The gun rights lobby is about to take aim again at a Sunnyvale law banning possession of large-capacity ammunition magazines, the latest standoff proliferating in courts around the country over the boundaries of the constitutional right to bear arms.

A group of Sunnyvale gun owners, backed by the National Rifle Association and other gun groups, on Monday will urge the 9th U.S. Circuit Court of Appeals to invalidate the city’s law, which was overwhelmingly approved by voters last year.

Gun rights advocates have thus far failed in their legal challenge to the ordinance, which threatens criminal prosecution of anyone with a magazine that can hold more than 10 rounds of ammunition. A San Jose federal judge upheld the law earlier this year, and the U.S. Supreme Court refused to put it on hold while the appeal unfolds.

The stakes could be high, as other California cities, including Mountain View, San Francisco and Los Angeles, have moved to adopt similar regulations. And given that the 9th Circuit shapes law for nine western states, its Sunnyvale ruling is likely to have a much broader reach.

To gun owners, the law is an unconstitutional slap at their right to protect their homes from intruders. To advocates of the law, it is a sensible response to gun violence, such as the tragedies ranging from the Sandy Hook Elementary School massacre in Newtown, Connecticut, two years ago to Gian Luigi Ferri’s mass shootings at a San Francisco law firm two decades ago.

The 9th Circuit is hearing the Sunnyvale arguments as federal courts across the country are dealing with the fallout from a 2008 Supreme Court decision that strengthened the Second Amendment right to have a firearm for self-defense. Emboldened by that decision, gun rights advocates have challenged state and local regulations in areas such as assault weapons and high-capacity ammunition rounds.

In one of these legal scrapes, the 9th Circuit just last week turned away the latest challenge to a recent ruling that loosened California’s restrictions on carrying concealed weapons, another issue that may eventually land in the Supreme Court.

Sunnyvale gun owner Leonard Fyock and other local residents took on Sunnyvale’s ammo law, backed by gun rights advocates insisting that millions of Americans own such magazines to protect “hearth and home,” as they told the 9th Circuit.

Chuck Michel, the NRA’s West Coast lawyer representing Fyock in the lawsuit, calls the case “pressing” to further clarify Second Amendment rights, noting that nearly half of ammunition magazines in circulation are capable of holding more than 10 rounds.

The organization clearly has an eye on the Supreme Court, recently adding Paul Clement, former U.S. Solicitor General during the George W. Bush administration, to the legal team.

“Anybody driving through (Sunnyvale) is at risk of being prosecuted (if they have these magazines),” Michel said.

Sunnyvale city leaders defending the law are backed by groups such as the Brady Center to Prevent Gun Violence. Sunnyvale pushed Measure C after the Sandy Hook shootings, in which 20 children were killed, arguing that such large-capacity magazines are unnecessary for self-defense.

“If you are going to argue there is a constitutional right to have virtually any sort of arms, even if there is no legitimate need for them, where do you draw the line?” asked Jonathan Lowy, director of the Brady Center’s legal action project. “They are not needed for lawful self-defense.”

California law since 2000 has banned making, selling, giving or lending magazines that can hold more than 10 rounds, but laws such as Sunnyvale’s go further by making it illegal to possess them in the home. It requires city residents to turn in illegal magazines or risk misdemeanor prosecution.

Cities such as San Francisco and Los Angeles have warned the 9th Circuit that overturning Sunnyvale’s Measure C would invalidate their campaigns to control gun violence.

Gun rights advocates, however, say the law is misguided. In an interview earlier this year, Fyock told this newspaper he hopes “somewhere down the line this will get overturned.”

One group backing Fyock in the court case calls Sunnyvale’s law “extreme.”

“In American history, magazine prohibition has been a rarity,” wrote the Gun Owners of California. “Sunnyvale’s (law) has no support in American legal history.”

Howard Mintz covers legal affairs. Contact him at 408-286-0236 or follow him at Twitter.com/hmintz.