Acording to a recent article, the hunter who recently died in a grizzly attack in Montana was killed by his partner's bullet, not the bear. See: http://seattletimes.nwsource.com/html/nationworld/2016301708_apushuntergrizzly.html

Alaska writer Craig Medred's article on this at http://www.alaskadispatch.com/article/think-gun-makes-you-safer-around-alaska-bears-think-again also includes a link to a study from the Journal of Wildlife Management on the effectiveness of bear spray. See: http://www.alaskadispatch.com/sites/default/files/Bear%20Spray.pdf