This is a good article GB sent me. Me personally, I wouldn't engage, unless there was immediate life in danger and the odds could be evened. My stance on self defense is get you and any family member or friend out of the situation. The odds and usually the weaponry are in favor of the active shooter.

https://chrishernandezauthor.com/2016/09/04/im-a-concealed-carrier-should-i-engage-an-active-shooter/