Gun-control advocates say magazines that can store and feed 30, 50 or even 100 bullets into firearms increase the potential carnage of an attack. It's believed that millions of such accessories are legally owned in the U.S. — prized by gun enthusiasts for recreational shooting and self-defense.
The U.S. Supreme Court is considering whether to take a case that revolves around the issue and asks if the Second Amendment gives people a right to possess the high-capacity ammunition magazines. So far, eight states have passed laws restricting magazine capacity to 10 or 15 bullets.
Magazines that hold 15 or 30 rounds are often considered standard equipment for new semi-automatic pistols and rifles, and are sold separately for as little as $15. Some drum-style magazines can carry 50 or 100 rounds.
Police have said they recovered several high-capacity magazines and thousands of rounds of ammunition from the hotel room and home of Las Vegas gunman Stephen Paddock. It's unclear how many rounds those magazines could hold, but cellphone videos taken by concertgoers recorded bursts of gunfire so rapid and sustained that it sounded like a battlefield.
Authorities say Paddock opened fire Sunday from broken out windows of his 32nd floor hotel room, killing 58 people and wounding hundreds more at an outdoor country music festival. Police stormed his room and found he had killed himself after committing the deadliest shooting in modern U.S. history.
Louis Klarevas, author of "Rampage Nation: Securing America from Mass Shootings," said it was likely Paddock was using some form of a high-capacity magazine because he fired so many rounds in a short period of time.
"That was non-stop rapid fire," he said. Nevada is one of 42 states — along with the federal government — that does not restrict the sale or possession of high-capacity magazines. The federal assault weapons ban of 1994 outlawed the manufacture of magazines that held more than 10 rounds, but Congress allowed the law to expire a decade later.
Klarevas said his research shows the use of high-capacity magazines has become more common since then in mass shootings. The magazines were used by gunmen who killed elementary school children in Connecticut and moviegoers in Colorado, among others.
Klarevas favors a federal ban on magazines that hold more than 10 rounds. California moved toward such a law last year after voters approved an initiative prohibiting people from possessing ammunition magazines capable of holding more than 10 bullets.
However, the law was blocked in June by U.S. District Judge Roger Benitez, who warned that it would turn law-abiding citizens into criminals if they didn't give up their high-capacity magazines. He intends to issue a final ruling later but believes the law will likely be declared unconstitutional.
Meanwhile, a coalition of gun rights advocates wants the U.S. Supreme Court to overturn a Maryland law restricting magazines that hold more than 10 bullets. A divided 4th U.S. Circuit Court of Appeals upheld the law.
The appeals court held that such magazines are most suitable for military and law enforcement purposes and are not protected by the Second Amendment. The court noted that Adam Lanza, who gunned down 20 first-grade students and six educators in Newtown, Connecticut, in 2012, was able to fire more than 150 rounds in less than five minutes.
Lawyers for Maryland argued that limiting shooters to 10-round magazines would allow bystanders and police more time to intervene or get to safety during pauses in firing. Maryland is among the handful of states to enact restrictions since the Newtown tragedy. Eight states now have restrictions on high-capacity magazines, according to the Law Center to Prevent Gun Violence, which calls the limits in California, Hawaii, New Jersey and New York the most comprehensive. Colorado and Massachusetts are the other states with restrictions.
The National Shooting Sports Foundation, the firearms industry trade group, opposes such laws. It has argued that the rules infringe on the rights of law-abiding citizens and do little to prevent crime.
It would not discuss its position in the wake of the Las Vegas attack. "Not now," spokesman Mike Bazinet said Tuesday. Former Connecticut House Speaker Brendan Sharkey, who helped enact his state's restrictions in 2013 after the Newtown killings, said he has heard no complaints about the law. He said there is bipartisan consensus that high-capacity magazines should be limited.
"The time has long passed for Congress to pass these types of restrictions," he said. "And in the absence of that, more states should."
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This story has been corrected to show that the death toll is 58, not including the gunman, based on revised information from the Clark County coroner.