It seemed to me the guy reaching really obviously behind for his gun in direct sight of the gunman got clipped first defensively by the shotgun guy?
Anyway, mindset of the shotgun man will make all the difference as to whether more guns saved or cost lives in this specific instance.
Back to my movie.
Indeed, that's what i saw, and what's more, the first parishioner to pull his gun told the gunman to "drop it". Otherwise the first person the gunman aimed at would have been shot first. No, i don't think you can say that his pulling his own piece started anything the gunman had not already intended. It just changed the order of the first two shots from the shotgun.