The Big Show Journal is no ordinary gun magazine. The print periodical, which appears on newsstands nationwide six times a year, is also, according to its website, "America’s most interesting gun and knife magazine" and "America’s most accurate and complete gun and knife show calendar." Gun enthusiasts may dispute the former claim—but the latter is less subjective than you might think.

In fact, The Big Show Journal might be the closest thing researchers have to a comprehensive record of gun shows in the US.

"There’s no readily compiled, publicly available database of where and when gun shows occur," says UC Berkeley epidemiologist Ellicott Matthay, who recently found herself in want of such a database. That includes the internet. When Matthay used the Wayback Machine to scour archived web pages for the dates and locations of past shows, she found gaps in the historical record; events she knew had happened were nowhere to be found. So she turned to trade magazines instead. The Big Show Journal, true to its claim, proved more comprehensive than competing publications like Gun List Magazine and Gun and Knife Show Calendar.

A state's gun laws, it seems, can be undermined by those of its neighbors.

Matthay needed that data to test a hypothesis about gun violence in America. Gun shows—of which the US sees about 4,000 per year—account for between 4 and 9 percent of firearm sales. As a public health researcher, Matthay knew that gun ownership increases the risk of suicide, homicide, and unintentional casualties in the home, and that firearms acquired from gun shows are disproportionately implicated in crimes. Matthay wanted to know if gun shows could lead to increased rates of gun violence, specifically in her home state of California. And the numbers she needed to find out were buried not in a government database, but in back issues of a big, glossy gun magazine.

But magazines are hard to mine for data. So Matthay set to work, scanning issues of The Big Show Journal published between 2005 and 2013 in the copy room at UC Berkeley's school of public health. She used optical character recognition software to convert the scans into alphanumeric data. Then she trained an algorithm to isolate the dates and locations of gun shows in California and neighboring Nevada, which shares the largest border with the state.

When Matthay was finished, she cross referenced her database with death records from the California Department of Public Health, along with ER and inpatient hospitalization records collected by the state. By comparing death and injury rates for the two weeks before and after each gun show, Matthay could see whether firearm casualties increased in nearby California areas in the wakes of California and Nevada gun shows.

Her hypothesis turned out to be half right: California gun shows did not appear to have a significant effect on local gun violence. But in regions near Nevada shows, rates of death and injury due to firearms spiked by 70 percent.

That staggering disparity could boil down to policy differences. California's gun laws are among the most stringent in the country. Nevada, in contrast, has some of the least restrictive—and no explicit regulations on gun shows. Data from the Bureau of Alcohol, Tobacco, Firearms and Explosives—which monitors where guns originate and where law enforcement recovers them—shows that firearms have a knack for flooding into states with tough gun laws from those without. (To cite just one example: Sixty percent of guns used to commit crimes in Chicago between 2009 and 2013 originated outside of Illinois.) A state's gun laws, it seems, can be undermined by those of its neighbors.

But that kind of inter-state analysis isn’t always possible. Many states—Nevada among them—don't require documentation of private gun sales.