I shoot them in the lungs behind the shoulder / front leg bones if they are directly broadside, with absolute confidence. The same as I do with sheep, moose, caribou, deer, mountain goat, or any other large game animal.
If they're quartering a little away or a little toward me from the directly broadside position, I shoot a little back or forward from dead center of the ribs/lungs. This has proven completely effective on two brown bears and over a dozen black bears, as well as every other big game animal I've shot in that location, provided the bullet expands on impact.
If shooting on the level at a broadside bear, center the animal from top to bottom and aim 5-10 inches behind the front leg bones. With any kind of an expanding bullet, even though the animal may run off a short bit before expiring, they're running dead on their feet. I can see how this can make a guide nervous and perhaps this explains their preference for breaking the animal down on the spot with the shoulder/bone shots.
I shot an above average-sized boar black bear at 425 yards two days ago. Bear was quartering away about 30 degree from directly broadside. 210 Berger VLD from a 300 Win Mag entered mid-way up on the bear at the location that the diaphram contacts the rib cage and angled forward through the chest cavity. The bear died on impact. The only movement was to collapse and then slowly roll 5 feet into the low hollow directly adjacent to where the boar had been standing. Often they'll motor 30 to 130 yds, but they will sometimes drop as if brained.
I shot a brown bear that squared 10' 5" on Kodiak Island through the center of the ribs from 130 yds with a 338 Imperial Magnum using a 225 grain trophy bonded bear claw bullet. The only movement that bear made was directly down to the ground like a sack of potatoes. I kid you not, that bear was killed on impact with nothing more than a hit to the center of the ribs. I waited a good 20 minutes before slowly approaching the boar because I didn't expect that reaction from a shot to the lungs. on an animal of that size. I had just about convinced myself the rifle's sights must have been off and I'd brained the boar. I walked up and the bear's head and skull were intact and I saw no visible sign of bullet entry or exit. Upon skinning I found the bullet entry hole exactly centered on the ribcage. There was no exit hole in the hide. I dug around insid the chest cavity searching for the bullet after skinning the bear but never found the bullet. I did get a good look at the inenr wall of the offside ribcage and there was no entrance wound there, so the bullet evidently didn't even penetrate to the opposite rib cage, which surprised me based on this bullet's performance observed a different brown bear a few years earlier.
I don't dismiss what these experienced big game guides are saying. I'm saying what I have done, and I'm reporting excellent results associated with it. Why don't I shoot them through the front shoulders? I eat the black bears and prefer to minimize the meat damage by slipping the bullet in behind the front shoulders. And the animals are deader than dead by the time I walk over to them.
As I have said, most often a strictly lung shot animal will run a fairly short distance before expiring. However ocassionally, they'll drop in their tracks as if they were struck by lightening. My best explanation from what I've seen and read is that the hydraulic shock of the bullet on the animal's central nervous system can simply overwhelm and short-circuit the body's nervous system. It can be as dramatic as if a "life" switch was flipped off.
Not trying to deminimize the advice provided by the guides or any other posters. They have good reasons for their preferences and recommendations - and alot of experience to back them up. If I was guiding bear hunter's I'd probably direct my clients to the same shot placement these guides are recommending. That way if the animal didn't drop at the shot, I'd have a good reason to suspect my client may have placed a poor shot, and I'd know it was time to cut loose to prevent an escaped, and wounded bear.
I started life as a bow hunter, always aiming middle of the rib cage and alway having success with those hits. I'm comfortable with the animal running off a short distance before bleeding out. If I was a guide, I wouldn't be too comfortable watching an animal heading for cover, not knowing whether it was wounded or as good as dead. Those same center of ribs hits with a rifle bullet later proved to work as effectively as the broadheads did, except occassionally, the shock effect of the expanding rifle bullet will flip the life switch off, instantly and dramatically.
