Here is an all too typical Twitter post making the claim that AR-15s are the weapon of choice for mass public shooters. But you have to wonder though if all this media coverage that these are the best weapons for mass public shooters actually causes more of these particular guns to be used than would otherwise be the case.
But this gives the false impression that these attacks were carried out with only AR-15s. Here is what the list should look like for these attacks.
Here is another way of looking at the breakdown of the rate that different types of weapons are used in mass public shootings.