You may well be right, but I came of age in the 1950s and I cannot recall any mass shootings during that time. Maybe there were and my memory is fauly. The first one I can recall occurring was in the early 1960s, that of the guy in Texas who placed himself in a college tower and randomly shot people with a rifle until the police shot him dead.
When that shooting started a student ran to his car and got out a 22 rifle and started to shoot back at the gunman. The student kept the gunman’s head down until the cops shot him.(the bad guy)