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Most gunshot victims and survivors were young minority men with prior court arraignments

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 use in AK-47-style rifles. While strictly speaking this round has a narrower diameter than even the medium calibers studied, 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 more deadly, resulting in odds of death 4.5 times that of small-caliber gunshots.

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“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.