As for the number 18 being thrown out for school shootings that is the ... way of saying a lie over and over until people start to believe it is true. And sad to say it works with many people.
The number originated from Everytown for Gun Safety and the number was derived from anything that had to do with a gun in and around. For your reading enjoyment....
http://www.washingtonexaminer.com/no...rticle/2649183