I can give you my opinions, which is based on some experience and actual observations for those who are wondering if I have any. Admittedly I have no experience on bear and cougar with a revolver. I would say just carry whichever is lightest and that you shoot well. If you want to buy another gun, so be it, it's a good excuse. As far as loads go, you will be much much more likely to need the gun on a human so I would go with an expanding type bullet like an XTP that can work on other critters as well if needed. Yes I have seen many people shot with expanding bullets, FMJ bullets and lead bullets from handguns, rifles and shotguns so I do have some experience. The expanding bullets have almost always done a better job of stopping a person because of more trauma, humans need comparatively little in the way of penetration like big game will.
I have seen many people who have been shot with many weapons, usually handguns, and have been in the middle of and actually witnessed a handful of shootings. Luckily I was armed with 00 buck for the most intense, very close range one. If I would have had just a handgun, I would have probably ended up very hurt or killed, even though he would have still likely been killed had I shot him many times with a handgun, he would not have been stopped by any handgun like the shotgun stopped him, which saved my butt.
Handguns are not death rays like on television and in fact in actual shootings, a human shot one time in the torso with a handgun has I believe (I am going from memory from a gunshot wound class from 3 years ago) a 97 percent chance of living. Additional rounds on target increase the chance of killing the subject exponentially. Remember, stopping power and killing power are two different things. Yes big bore revolvers with heavy cast bullets are very good killers even for very large animals, they however lack the high velocity that causes massive trauma that is usually what stops. This does not inclued a proper central nervous system shot, which will almost always stop even with a handgun, almost.
You have to take into account the motivation and state of the animal you are up against. Lucky for us, the vast majority of people who are shot will fall to the ground screaming with even a minor injury to an extremity, because humans are soft. This is where the high percentage of one shot stops comes from associated with the rating of handgun loads in actual shootings. Many of these people were still not killed, just stopped. If you take a motivated, demented, high, mental or deranged subject or just one who is dedicated to the cause, we have a different subject all together. In this case anything short of a central nervous system shot will do nothing until they bleed out or are broken down by hitting pelvis, major bones or other parts of their frame, which will drop them but still not always stop them as they will crawl or fight from the ground if they are dedicated enough.
All this said, I am definately not saying I'm an expert, just my experiences. Carry what you are most comfortable with and if in the unfortunate and unlikely chance that you have to shoot, shoot until your gun is empty or until someone is on the ground and no longer a threat.
We all have our opinions, some are based on experience, too many are based on internet forums. There are many answers on here for you to choose from. The most important thing is to have fun on your hike.
