The magazines aren't tracked. But there are plenty of anecdotal indications that the floodgates briefly opened when U.S. District Judge Roger Benitez overturned the state's nearly 20-year-old ban in late March.

Gun control advocates, however, said the projections are inflated and self-serving as gun rights organizations try to make the case that high-capacity magazines bans are impractical.

The judge halted sales a week later, but ruled that those who bought the magazines can legally own them while the state appeals his ruling.

"Everything was all sold out. I basically took whatever I could get," said Chris Puehse, who owns Foothill Ammo in Shingle Springs, east of Sacramento.

He fielded dozens of telephone calls while buyers stacked up 20 deep in his one-man store to buy the hundreds of magazines that arrived in two shipments last week. He had just six left by the time Benitez reinstated the ban last Friday.

"People loved it. It was like we were out of prison and were not treated like bastard stepchildren of the country anymore," he said.

Puehse said that 30-round magazines for military-style rifles, handgun magazines holding 17 to 20 bullets, all selling for less than $30 each, almost immediately "disappeared.”

"They wanted to grab more than I let them, otherwise they would have been gone even faster than a few hours,” he said. "Because of that one slip-up, in one week you literally had millions of magazines come into the state that were bought legally. These magazines are here to stay."

Hours before Benitez again halted sales, California Attorney General Xavier Becerra warned that the state was in danger of becoming "the wild, wild West for high-capacity magazines."

"There are those who are now trying to flood the state of California with what were until this decision illegal high-capacity magazines, the type of magazines that are used in firearms to commit the mass shootings that we've seen throughout the country," Becerra said.

The magazines allow shooters to fire more bullets without stopping to reload. Gun owners' organizations — and Judge Benitez — said that's helpful to ward off multiple home invaders, but opponents said it gives victims less time to escape or tackle a mass shooter as he reloads.

During that short window, a number of ammunition manufacturers around the country sought to take advantage of the opportunity. South Carolina-based Palmetto State Armory announced in a Facebook ad that it was "prepared to send a whole lot of freedom to our friends in California," but warned of delays due to high demand.

"The pipeline was open and it was flowing, on all platforms — people showing up (in stores), online — I'm guessing that UPS and FedEx had a field day," said Gun Owners of California president Sam Paredes. "It was a frenzy."

He said an estimate of a million magazines "seems a little bit low."

California's more than 2.5 million gun owners together have nearly 20 million guns, many of which can use the extended magazines.

Staff attorneys with the Giffords Law Center to Prevent Gun Violence in San Francisco said they've seen no evidence to back up the million-magazine estimate, and said gun rights organizations have a vested interest in inflating the number of law-abiding owners.

"They have a very specific purpose and intent here to try to set up for the court that these are devices that are very commonly used and possessed" and therefore should not be banned again, said Ari Freilich, an attorney with the center.

The problem isn't the new owners who will use them legally for target shooting or self-defense, he said, it's that some will fall into the hands of criminals or be used by mass shooters.

Reformers expect the 9th U.S. Circuit Court of Appeals to keep the ban on sales while reinstating a 2016 state law and ballot measure banning possession even by those who purchased the magazines legally.

Opponents of California’s law are counting on the U.S. Supreme Court to ultimately side with Benitez's ruling, that the bans infringe on the Second Amendment right to bear arms.