The United States now has more than one gun for every American adult.

American gun stockpiles swelled by 70 million guns to a total of 265 million over the past 20 years, even as violent crime rates fell, according to a study by researchers at Harvard and Northeastern Universities.

Of those, between 300,000 and 600,000 guns are stolen every year.

Despite the more than one-to-one ratio, half of those guns are owned by 3 percent of Americans—7.7 million "super-owners"—who own an average of 17 guns apiece, according to the study, an online survey of about 4,000 Americans conducted last year.

Those super owners have between eight and 140 guns each, while almost half of gun owners had only one or two guns.

The survey, which has not yet completed a peer-review, also found that while the number of guns in the U.S. has increased, the percentage of ownership fell from 25 percent of Americans in 1994 to 22 percent in 2015. Currently, about 55 million Americans own guns. Those gun owners "tend to be white, male, conservative, and live in rural areas," the study found.

More precisely, the study found 25 percent of gun owners are "white or multi-racial," while 16 percent are Hispanic and 14 percent African American.

The number of handguns grew from 65 million in 1994 to 111 million in 2015—a 71 percent jump.

“In a country where 35,000 people a year die by firearms, we haven’t been able to come out with a survey on gun violence for 20 years,” said Deborah Azrael, director of research at the Harvard Injury Control Research Center. “That’s a real failure of public health and public policy.”