This story was published in partnership with the Trace.
There is no official count of how many guns Americans own. But the best available calculations make it clear that the number has grown by tens of millions in recent decades, leaving the United States ever more densely armed than other countries.
A June 2018 report from the Small Arms Survey estimates that American civilians own 393 million guns, both legally and otherwise, out of a worldwide (civilian) total of 857 million firearms. That’s up from 270 million civilian-owned guns domestically, and 650 million globally, in 2007, the last time the Swiss organization released an estimate.
The report shows that not only has the total number of guns owned by private citizens in the United States gone up, but so has the country’s share of the global total: from 42 percent a decade ago to 46 percent today.
"The biggest component driving up the number of guns in the world is American civilian buying," said Aaron Karp, the report's author.
Both domestically and globally, guns kill more people than any other kind of weapon. But because they are smaller, cheaper, more widely produced and less regulated than other weapons, they are inherently difficult to track. In the United States, a hard count of the civilian arsenal is impossible: A federal law fought for by the National Rifle Association prohibits a central registry of firearms possessed by private owners. (The Bureau of Alcohol, Tobacco, Firearms and Explosives, which regulates gun sales, even faces severe restrictions on how much it can digitize its records of firearms transactions, lest they form a de facto national gun inventory.)
As a result, experts have to make estimates of privately-owned guns using wildly different data and methodology, and they can reach widely varying conclusions.
The Small Arms Survey count is significantly higher than one produced by the National Firearms Survey, a joint project of Harvard and Northeastern University, which in 2015 estimated that American civilians owned 265 million guns. Its authors calculated that the nation’s firearms stockpile had increased by only about 70 million guns since 1994, the last time a detailed, nationally representative survey was conducted, by researchers Philip Cook and Jens Ludwig. The study showed the percentage of Americans owning guns as essentially flat. The rise in privately-held guns came from the emergence of hardcore firearm aficionados who represent just 3 percent of all gun owners but individually possess an average of 17 guns each and collectively account for half of the civilian stockpile.
The 2015 National Firearms Survey was based on direct surveys of individual gun owners. Researchers took respondents at their word about how many weapons they owned.
The Small Arms Survey combined and weighted a wider array of sources, including government registries in other countries, academic surveys like the NFS, law enforcement and manufacturing data, and other proxy measures.
Both methods are ways of working around the absence of reliable government data. "There's no standardized international reporting system," Karp said. "A lot of countries do nothing to keep track of their civilians' guns."
In the American gun world, estimates are even higher. Some ideologically-motivated firearm advocates assert that American civilians own as many as 600 million guns.
Complicating matters further is how or whether estimates account for the number guns that fall out of circulation. The National Firearms Survey, along with researchers Ludwig and Cook, factor a 1 percent annual depreciation rate to the gun supply, to account for the disposal of older guns. But Deborah Azrael of Harvard, who co-authored the NFS report, says the actual rate could be lower. "Nobody really knows how many guns leave circulation each year," she said.
Knowing the total number of guns in civilian hands isn't just an academic pursuit. It has implications for law enforcement and public safety policy, since clear records of who owns which guns would make it easier to trace crime weapons and disarm people who commit offenses that make them ineligible to possess guns they had previously lawfully purchased. In the United States, estimates of privately-owned guns have political ramifications, too, as candidates and voters debate whether guns should be harder or easier to acquire
"It will be interesting to see how this new estimate is used," said Karp. "For some people, it will be irrelevant. For others, it will be instrumental."
This article originally appeared on VICE US.