I would venture to say that most of these spree shootings could of been negated or terminated if a law abiding citizen engaged the shooter. How many active shootings have happened at a gun shop?
You do realize that "active shooting" means the period of time in which shots are being fired, right? So lots of "active shootings" have happened in gun shops, but not too many mass shootings. Of course, there aren't all that many gun shops and of the ones that exist, most are fairly small operations. Given that mass/spree/rampage shooters tend to do their deeds where they have some direct connection, usually where they have had or perceive to have had some sort of trouble or conflict.