but I was told of a fishing guide who was attacked and put 4 rounds of .44 mag in the body with no immediate effect. The attack was halted by another guide who sprayed the bear.
Possible. I actively search for these stories, and I have not seen it.
I have seen a few where the spray does not work, but a firearms does.
Interestingly, I have not found one case where a pistol failed to stop a bear. At least not yet.
http://gunwatch.blogspot.com/2016/10/where-are-bear-attack-pistol-failures.html
Efficacy of Firearms for Bear Deterrence in Alaska
AbstractWe compiled, summarized, and reviewed 269 incidents of bear-human conflict involving firearms that occurred in Alaska during 1883-2009. Encounters involving brown bears (Ursus arctos; 218 incidents, 81%), black bears (Ursus americanus; 30 incidents, 11%), polar bears (Ursus maritimus; 6 incidents, 2%), and 15 (6%) unidentified species provided insight into firearms success and failure. A total of 444 people and at least 367 bears were involved in these incidents. We found no significant difference in success rates (i.e., success being when the bear was stopped in its aggressive behavior) associated with long guns (76%) and handguns (84%). Moreover, firearm bearers suffered the same injury rates in close encounters with bears whether they used their firearms or not. Bears were killed in 61% (n = 162) of bear-firearms incidents. Additionally, we identified multiple reasons for firearms failing to stop an aggressive bear. Using logistic regression, the best model for predicting a successful outcome for firearm users included species and cohort of bear, human activity at time of encounter, whether or not the bear charged, and if fish or game meat was present. Firearm variables (e.g., type of gun, number of shots) were not useful in predicting outcomes in bear-firearms incidents. Although firearms have failed to protect some users, they are the only deterrent that can lethally stop an aggressive bear. Where firearms have failed to protect people, we identified contributing causes. Our findings suggest that only those proficient in firearms use should rely on them for protection in bear country. Efficacy of Firearms for Bear Deterrence in Alaska (PDF Download Available). Available from: https://www.researchgate.net/publication/261982557_Efficacy_of_Firearms_for_Bear_Deterrence_in_Alaska [accessed Nov 12 2017].
And, of course, there are incidents like this. Teenager Killed by Polar Bear Because Adult Forgot To Turn Off Mauser 98K Safety