I have never hunted grizzleys, but i have killed my share of black bears. Been up close and personal to a few a time or two. Two or three times I didnt even have a gun. I understand the big gun theory, I know one that was shot 5 time with a 44mag in the white spot on its chest that almost got my hunting buddy, bear caught a dog and gave my buddy time to load one more bullet in the ruger carbine which he stuck to its head and pulled the trigger. I posted some pics a couple years ago where another buddy shot a 760lb Bbear with a 458 and the bear still got him and almost tore his leg off. I know of a time a bear was shot in the shoulder and the bullet didnt even break the bone. I know a guy that put 10 rounds from a 9mm carbine and never slowed the bear down, it was finished off with a 44mag. My first bear I killed with a 30-30, everyone since I used my 44 ruger, one with my model 29 smith. A lot of guys I hunt with have all went to the 45-70. I have considered getting one myself. I figure I dont bust the brush anymore and any shot I might get is of a bear up a tree, head shots aint that hard from that distance. One thing I am pretty sure of is if a bear is mud fat, it hard to get good penetration, I suspect the same for a grizz. Shoulder shots and body shots , even with a big caliber, might not make it to the vitals. I found 180grain wad cutters penetrate deeper than the 240 grain 44s. I think if I was to go on a grizz hunt, I would go for one the 250grain bottleneck cartridges before I would go for one of the 3-500 grain straight wall cannons.