Hack recommends the 41mag or 10mm as the marginal starting point for handguns against bears. MUCH better are the 44mag, 454, 480 class of cartridges. He has hunted, guided, and followed up wounded bears lost by other hunters with a 7.5" 44mag SRH. He has also used a S&W 4" Mod. 29, but limited range of shots with the shorter barrel. He claims IMPACT velocity, not MUZZLE velocity, must well exceed 1000fps as a minimum. He says the ultra class is the S&W 500, 460, etc.. Contrary to popular wisdom (and he is personal friends with Randy Garret and has discussed the topic energetically with same), he does not recommend hardcast solids for bear hunting much less bear stopping. Again, they will kill, but take a long time to do it unless you take out the CNS. He recommends and used the 44mag class and up for bear protection on bears up to 500 pounds, not the really big bears, He does not recommend handguns for stopping the big bears, although it can be done with a CNS shot. He says if you can reliably hit a softball bouncing toward you at 30 MPH, then you might want to consider yourself ready to stop a big bear with a handgun. No professionals do with the big bears, although he did as a professional with black bears.
The reason he claims he did use a handgun to reliably stop black bears, and the reason he used heavy, expanding 44mag bullets, not solid hardcast is this. Evidently, when you shoot a black bear with a heavy expanding bullet moving more than 1000fps on impact, the bear with stop or spin, because of the stunning, hydrostatic shock of the impact, enabling you and/or others to get away in a defense only scenario, or better, follow up shots to kill the bear.