A new study published in the journal JAMA Network Open underscores an often overlooked factor in gun-policy debates: When it comes to lethality, not all guns are created equal.

Analyzing data on hundreds of shootings in Boston from 2010 to 2014, Anthony Braga of Northeastern University and Philip J. Cook of Duke University found that on a bullet-per-bullet basis, shootings committed with a large-caliber firearm are much more likely to result in a fatality than those with a smaller-caliber gun. Caliber is a measure of the diameter of the bullets fired by a particular gun.

The study analyzed data on 221 gun homicides and 1,012 nonfatal shootings that happened in Boston between 2010 and 2014. On first glance, the numbers provided a confirmation of the depressing demographics of shooting cases: “Most gunshot victims and survivors were young minority men with prior court arraignments,” Braga and Cook found. “Most attacks occurred in circumstances where gangs or drugs played an important role.” Most occurred outdoors in disadvantaged neighborhoods.

But they found stark differences in shooting outcomes depending on the caliber of gun used. They divided the calibers of guns used in the shootings into three categories: small, which included .22-, .25- and .32-caliber handguns; medium, including .380s, .38s and 9mms; and large, including .40s, .44 magnums, .45s, 10mms and 7.62 x 39s.

That last one is the type of round used in AK-47-style rifles. Strictly speaking, this round has a narrower diameter than even the medium calibers studied, but the authors say they categorized it as large-caliber because of the increased bullet velocity provided by the round’s large cartridge, which contains a relatively high volume of gun powder. Of note, there was only one shooting involving that kind of weapon in the data set. All the other shootings involved handguns.

They controlled for a number of other factors, such as circumstances of shootings and the number of times victims were shot. They then found that all else being equal, a person shot with a medium-caliber weapon, such as a common 9mm handgun, were roughly 2.3 times as likely to die of their wounds than someone shot with a small-caliber gun. Large-caliber gunshots were even deadlier, resulting in odds of death 4.5 times that of small-caliber gunshots.

“The implication,” they write, “is that if the medium- and large-caliber guns had been replaced with small caliber (assuming everything else unchanged) the result would have been a 39.5% reduction in gun homicides” in Boston during the study period.

The results undercut the idea that “guns don’t kill people, people kill people.” That catchy turn of phrase is often used by gun rights supporters to emphasize the human role in gun violence rather than the gun itself. The idea is that the gun matters a lot less than the murderous intent of the person pulling the trigger. If the person matters more than the gun, in other words, it’s better to focus policy on people than to regulate guns.

This view is widespread among experts who take a permissive attitude toward gun regulation. A Rand Corp. study published earlier this year, for instance, surveyed a group of gun experts who generally favored fewer gun restrictions, asking what would happen if a given gun policy was successful at reducing gun homicides. On average, those experts believed that about 90 percent of the prevented gun homicides would simply end up as homicides by other means. That reflects a belief that homicidal intent is the key factor driving the lethality of gun violence.

But the JAMA study challenges that notion. Some guns are simply manufactured to be more lethal than others. It suggests that identical shooters with identical intent would kill fewer people if they had access only to less powerful firearms.

“The probability of death is connected to the intrinsic power and lethality of the weapon,” Braga and Cook write. “That suggests that effective regulation of firearms could reduce the homicide rate.”