The Federal 410 1/4 oz slug is better than you'd think. I wouldn't hesitate to take on a caribou with this load. Penetration is about 60% of a 12 Gauge 1 and 1/4 oz slug. I haven't found any 1/4 oz Brenneke's but they might even be better.
On bear.... no way reliable enough as the 110 grain soft slug can fragment badly on bone and doesn't give much of a wound channel for instant kills. The buckshot would seem to be better as the 5, 00 loads have a pretty impressive total weight but they penetrate even worse than the slug on a hard target.
By the way the fairly sedate (for a rifle)44 magnum in the above test out-penetrated all the shotgun ammo, even the 22 Hornet came close. Rifle a better choice for defense than a shotgun IMO. I use a 450 Marlin as my out-fishing gun.