Attendees try out model pistols at a gun show on January 17th, 2012, in Las Vegas, Nevada. (Photo: Ethan Miller/Getty Images)

The unwillingness of Congress to strengthen gun-control laws, even in the wake of such tragedies as the recent mass shooting in Las Vegas, has led frustrated activists to focus on the state level. But in our mobile society, the state laws—however strict—can be circumvented by the ability to buy weapons more freely just across the border.

A newly published study presents evidence that the impact of looser gun regulations can bleed over into a neighboring state (to use a grisly but apt metaphor). It reports that, in the weeks following a gun show in Nevada, gun-related injuries rise in adjacent areas of California.

While this spike is relatively small, it does not occur after California gun shows, which are much more tightly regulated than those in Nevada. This suggests the state's relatively strict guidelines on gun purchases have a positive impact, but their effectiveness is diluted by the ability to freely purchase firearms just over the state line.

"There are thousands of gun shows in the United States each year, most of them in relatively unregulated states," said the study's senior author, Jennifer Ahern of the University of California–Berkeley. "If we extended this study nationwide, it is possible that the number of deaths and injuries associated with gun shows would be far greater."

The study, published in the Annals of Internal Medicine, examined the impact of 915 gun shows held between the years 2005 and 2013—640 in California and 275 in Nevada. The researchers analyzed gun-related deaths in injuries in California zip codes that were within a one-hour drive of California gun shows, or a two-hour drive of Nevada gun shows.

They specifically looked at the difference in deaths and injuries in the two weeks before the show, and the two weeks after it occurred. (For California shows, the "after" period began 10 days following the event, to account for the state's waiting period for gun purchases.)

"Firearm injuries in California remained stable after California gun shows, but increased by a small but significant amount after Nevada shows," the researchers report. They add that the Nevada spike "was driven by significant increases in firearm injuries from interpersonal violence."

The research team, led by Ellicott Matthay of UC–Berkeley, notes that all firearm sales at California shows must be "documented by a licensed dealer and include a background check." These safeguards are not required in Nevada.

Amazingly, that is due, at least in part, to a bureaucratic dispute. Last November, Nevada voters approved a ballot measure expanding background checks, including at gun shows. But the law has yet to be enforced, due to a dispute by state and federal officials over who should perform the background check on private gun transfers.

"Laws regulating access to guns matter, and do make a difference, especially collectively," University of Washington researchers Ali Rowhani-Rahbar and Frederick Rivara write in an editorial accompanying the study. "However, their impact on an individual basis is a somewhat small chip in the granite wall of firearm injuries and deaths. "The state-by-state nature of these laws, due to the lack of federal legislation, results in barriers to gun access that can be easily breached by a car trip."

When it comes to guns, what happens in Vegas doesn't always stay in Vegas.