From The Truth About Guns:

For example, despite what you have been led to believe and contrary to sensationalized reporting, mass shootings are not more frequent today, only more publicized and propagandized.
Northeastern University Criminal Justice Professor James Fox reported that the highest casualty rate for mass murders in the past three decades occurred in 1977. In that year, 38 criminals killed 141 victims. Compare this to 1994, which had the lowest number of mass murders: 31 criminals murdered 74 people.