(CN) — Posing hypothetical questions about the “slippery slope” California’s voter-approved ban on gun magazines with over 10 rounds of ammunition could have on gun owners’ rights, the Ninth Circuit considered Thursday whether Proposition 63 was unconstitutional.

Appealing U.S. District Judge Roger Benitez’s decision last year striking down the 2016 law passed by 63% of California voters, Deputy Attorney General John Echeverria said the ban was enacted to protect residents and reduce casualties in mass shootings.

The law was challenged by gun owner Virginia Duncan and the California Rifle and Pistol Association in 2017.

U.S. Circuit Judge Consuelo Callahan, a George W. Bush appointee, echoed Benitez – also a Bush appointee – when suggesting via teleconference Thursday that residents who become victims of a home invasion might not be “a great shot” and may need enough rounds to take down a home intruder.

“There seems to be some evidence that people need more than a few bullets to defend themselves in the home,” Callahan said.

Echeverria pointed to evidence an average of 2.2 rounds is fired during a home invasion — far fewer than the maximum rounds allowed under state law.

But Callahan said the 10-round ban “seems to be a random choice,” given many firearms commonly owned for self-defense purposes can hold 16 or more rounds.

“It sounds like a pretty slippery slope,” Callahan said before asking Echeverria to concede a magazine ban above zero rounds of ammunition would be “too low.”

Echeverria agreed zero rounds of ammunition would be “too low,” noting there are “some rights” in being able to operate a firearm using a magazine.

U.S. Circuit Judge Kenneth Lee, a Donald Trump appointee, pointed out in the evidence cited, in 14 of 17 mass shootings in California more than one gun was used. He asked Echeverria whether a ban limiting one gun per household would pass the constitutional muster he claimed Proposition 63 did.

“I think there’s a possibility that could trigger heightened scrutiny. That law would be much more burdensome than the law here,” Echeverria said.

Callahan pressed the issue. “What if my husband and I both want a gun, and we have to share one and decide who gets to shoot, and by then we’ve been shot.”

But Echeverria disputed the ban on high-capacity magazines was analogous to a ban on how many firearms one could own. He noted Californians can own as many 10-round magazines as they want and store them in their home in any way they choose.

Responding to Callahan’s question about “what’s the magic” of having the limit at 10 rounds, Echeverria said it’s intended to create lifesaving “pauses” during a mass shooting, when a shooter without access to high-capacity magazines would have to pause and reload their firearm – giving a chance for victims to escape.

“These pauses save lives. They saved lives in Vegas. They saved lives Thousand Oaks. They saved lives in Tucson,” Echeverria said.

Erin Murphy, representing Duncan and the California Rifle and Pistol Association, said Proposition 63 was unconstitutional because the law was not narrowly tailored to serve the government’s interest in protecting citizens from gun violence.

“We don’t dispute there’s a compelling interest in protecting Californians and trying to reduce gun violence and in trying to decrease the lethality of mass shootings when they do occur. We don’t dispute those are important or compelling interests,” Murphy said.

“What we take issue with here is whether the means the state has chosen are means that are appropriately tailored to serve that interest and do so without unnecessarily abridging more constitutionally protected conduct than necessary,” she added.

Murphy said California’s high-capacity magazine ban does not pass the U.S. Supreme Court’s Heller test, which held commonly owned weapons by law-abiding citizens are protected by the Second Amendment.

Tens of millions of high-capacity magazines of more than 10 rounds are lawfully possessed, Murphy said.

“It’s just absolutely clear that by sheer numbers and the amount of magazines purchased, whatever that number is, 10 can’t be the limit,” Murphy said when responding to a question by U.S. District Judge Barbara Lynn, a Bill Clinton appointee sitting by designation from the Northern District of Texas.

Murphy said the ban violated the Takings Clause of the Fifth Amendment even though Californians can own as many 10-round magazines as they want. She said the Constitution protects the right to own a firearm that can shoot more than 10 rounds of ammunition without having to reload the weapon.

She said the evidence that “pauses” in mass shootings save lives “is not reliable in and of itself.”

But on rebuttal, Echeverria said the state doesn’t have to show causation, just correlation in reduced deaths due to “pauses” in mass shootings.

He said Benitez “did commit clear error by ignoring all of the expert testimony” the state presented on mass shootings in his summary judgment before he was cut off by Callahan who said she’d given him extra time and was “going to call it a day.”

The matter was taken under submission.