That is the new article by Michael Rosenwald, here is an excerpt:
From 1976 to 1994, there were about 18 mass shootings per year, according to Fox’s data, which is drawn from federal statistics. Between 1995 and 2004, a period covering the ban [on assault weapons], there were about 19 incidents per year. And from 2005 to 2011, after the ban expired, the average went up to nearly 21.
Fox makes an important point about what probably happened during the ban: Mass shooters can rather “easily” come up with “alternate means of mass casualty if that were necessary.”
In other words, if they can’t get an AR-15, they get a Glock.
Assault rifles are used in only about 27 percent of mass shootings, see Alex too.
Here is an additional piece worth reading: “common state and federal gun laws that outlaw assault weapons are unrelated to the likelihood of an assault weapon being used during a public shooting event. Moreover, results show that the use of assault weapons is not related to more victims or fatalities than other types of guns.”
There is more here.