The short answer: no.
The long answer:
Look, a bear is big, mean, tough, big, mean, and tough. Some have likened it's skull to 'armour plate' while others have claimed that bears are as big (and a whole lot tougher) than a VW bug. Don't mess with a bear. Period. All a 9mm/7.62*39/.357/.45ACP/etc. will do is annoy it, at worst. If you are lucky, it will ignore it and not notice you. Bears can travel at 30mph+, so don't even think about such fanciful things as, "I'll shoot it in the eye." If you want to hunt bear, bring a BIG, BIG caliber - try at least .338 Winchester Magnum, maybe more. Forestry types usually carry at least .357, more often .44 magnum, and that is only for emergency situations.
Let me begin this by stating that I have no first hand experience dealing with bears. Having grown up in and around the town of Cordova on Prince William Sound in Alaska, hunting, fishing and otherwise spending a lot of time in some very serious brown bear country I consider this a fortunate accomplishment. I know several people who have had close bear confrontations, and once I was very close to three (yes, three) brownies while ATV riding and did not find out until afterward. This article is intended not as a comprehensive guide to living in bear country, however I will discuss some of the more important concepts, as well as some other things that I have picked up over time.
More often than not, a bear will take every opportunity to avoid contact with human beings. Unfortunately this is not always the case; when dealing with bears there are only two things which may be depended on. First, any bear is going to be a whole lot bigger and meaner than you are except for cubs, in which case you have an even bigger problem. Second, a bear is an intelligent and unpredictable animal, notorious for behaving in a completely unexpected manner.
There are many differing opinions about what makes a suitable bear defense gun, but the truth is that so long as certain guidelines are adhered to, the actual caliber selection is not all that important. Bears, especially brown bears (referring to the species, both black bears and "grizzlies" can range in color from tan to dark black), have a nasty ability to absorb amazing amounts of lead with no apparent loss of power or mobility. There have been many cases of attacks in which a mortally wounded bear has continued to maul its victim(s), before crawling off to die itself, even when hit in the vitals with a "stopping" rifle caliber. The following are my opinions only on what makes a suitable bear defense gun, and should be treated as such.
From what I have observed, opinion seems to be fairly evenly divided between those favoring the use of a high-powered rifle and those advocating 12 gauge slugs, with the rifle faction holding a slight edge. With a shotgun, you will want a pump action with a fairly short barrel using foster-type slugs, extended magazine optional. Unless you are highly trained in their use, stay away from pistol grips; while they make carrying it much easier, in the unlikely event that you need the gun they could easily cause you to miss, and with a bear you will not get a second chance. If you choose to carry a rifle, a good reliable bolt action in the 7mm, 30-06 range on up should be adequate, the upper limit determined by the competence of the shooter. If you can handle the larger calibers then go ahead and use them, but with bears bullet placement is MUCH more important than incremental increases in power. Stick to the heavier bullets for a given caliber; you want all of the penetration you can get. For a pure bear defense weapon, stay away from scopes. Open sights are much faster, and within the close ranges at which bear defense takes place, they are more than adequate; whereas a scope in which you can see nothing but indistinguishable hair is useless. I would not choose a semi-automatic rifle or shotgun, besides being heavier to carry around, to me the possibility of a jam is unacceptable. My personal choice is an old, beat up Savage 110 in .30-06 with open sights, though I have often considered putting a shorter barrel on my 12 gauge and using it instead.
Pistols are a really bad idea for bear defense, in my opinion. While some pistols are certainly better than others, these are generally much more difficult to control than a rifle, while being much less effective. The only times when I would consider a pistol is if I were involved in some activity which made carrying a rifle not only impractical, but impossible. One example of this type of situation is my brother, who often fishes from a float tube or with chest waders in deep water. I avoid the problem by using a canoe. Out of the people I know who do carry pistols for bear protection virtually all of them have a rifle or shotgun of some kind nearby, and the pistol is only a backup weapon. A good minimum pistol caliber is .44 Magnum, though some are comfortable with a .357.
You have probably figured out by now that I do not place a lot of faith in being able to reliably stop a bear intent on killing a person, even with a suitable weapon. While I do not often venture away from my vehicle without being armed, and certainly not during the summer when the bears are out in force to munch salmon; I view a bear gun as only a backup to be used if everything else goes wrong. The only proven way of avoiding trouble in bear country is to not come into contact with bears to begin with. There are many successful techniques to minimize the chance of running into a bear, all of them involving common sense and caution. The following are several rules which can keep you out of trouble, if I have overlooked anything, please feel free to comment.
Try to make as much noise as possible, the farther away you are when the bear hears you coming the more time it has to get out of your way.
Keep all food in airtight containers, so that the bear does not smell it and decide that it would make a good "free lunch."
Avoid areas such as salmon streams, alder thickets, berry patches and dumps. With experience you will be able to spot areas with "bear" written all over them.
Avoid any area in which you cannot see what is around you, even if it means taking the long way. The farther away you spot a bear or it spots you, the more time you have to get out of each other's way. Of course, the bear should hear you long before you see it (see above).
When making camp, avoid the areas listed above, and be sure to avoid camping on or alongside trails of any sort. Bears will use trails just as humans do, and you do not want a bear to come strolling into your camp just because you put it in the wrong place.
Keep any food in airtight containers OUTSIDE OF CAMP, and out of reach of bears. This means way up high. Also, it is best to do your cooking away from where your camp is located. Humans aren't the only ones attracted to bacon frying in the morning.
If you see any bear cub(s), or a mama bear with cub(s), or even suspect that there may be any in the area (i.e. see tracks, or hear from others who have been in the area) then get the heck out. A bear will defend her cubs with everything she has, usually with a kill first, ask questions later philosophy. Even if you don't think you are bothering them she will probably have a differing opinion.
When beaching a boat, it is best to pick an open area or beach to do so, or in the words of my dad, "don't go ashore into that brush, there could be a bear a-lurkin' there."
If possible, I prefer to travel by boat or floatplane, that way you only have to worry about bears at your destination, and not en route. These each have their own hazards, however.
If possible, bring friends. More people equals more noise, and more firepower as well. However the most important aspect of having companions is psychological, when you are alone each noise becomes a bear, the dark is darker and the cold feels colder.
I have probably overlooked several things, but to me these are some of the most important. Bears being unpredictable by nature, there are times when even the most careful person will have no choice but to use a weapon against a bear, and in this case what we are looking for is NOT volume of fire. You want to damage the bear in such a way that it will be unable to continue its attack, this means damaging its skeletal structure or central nervous system so that it is physically incapable of moving toward you. A heart shot will probably kill it, but not necessarily before it kills or seriously injures you. I am not an expert on bear anatomy, but in this situation I would want to aim for the front shoulders if possible. Do not try for the head, a bear's skull is thick and has been known to deflect bullets. If you manage to put it down, do not assume it is dead. Put several shots into the head and spine, and while reloading get to a good position of observation far enough away that if it is not quite dead you will not be in immediate danger, and wait for a few minutes to be sure it is dead. Your actions at this point will be determined by the extent of the injuries of any members of your party, and the laws of your jurisdiction concerning destroying a bear in self defense. As with any animal wounds, any wounds dealt by the bear should be thoroughly cleaned and disinfected, you do not know what bits of rotting matter are under an animal's claws; in any event seek medical attention ASAP. Before venturing into bear country know what is legally expected of you in this scenario.
I sincerely hope that this article does not serve to discourage people from entering bear country. While I believe all of the above to be true, the possibility of a bear attack, even in serious bear country is very small, so long as a person takes the correct precautions. As a general rule bear country is also the most beautiful rough country in the world, and a person would be a fool to let the presence of bears discourage them from experiencing it. As far as I am concerned there are only 3 things necessary when traveling in bear country; A proper weapon which you can use skillfully, a healthy respect for the bear and its abilities, and above all else an appreciation for the countryside which you are traveling through.
One other thing, be sure to remove the front sight from any bear defense gun. That way it will not be as painful when the bear shoves it up your.......
(just kidding)
Recommended reading:
Alaska Bear Tales, by Larry Kaniut. A book of mostly true stories about bear experiences which will help to give the reader a better understanding of the nature of bears and bear defense. There is also a sequel out entitled "More Alaska Bear Tales."