Why more people are dying from shootings: bigger guns, bigger bullets

It wasn't clear to me why murder rates have been going up in those cities with a higher propensity for violence, including DC (although the murder rate in the city is about one-third of what it was in the early 1990s).

Recently, DC's police chief Peter Newsham was quoted as saying that the number of shootings has been relatively constant, but more people are dying.

Then the New York Times reported ("'Type of Weapon Matters': Linking Caliber Size to Death Rate") on a study of homicides in Boston over a six year period.  The study found that the number would have been 40% less if smaller bullets would have been more prevalent.