Never hunted grizzly never will, but a 338 win mag with a 250 grain nosler partition and Federal High energy ammo would be a good choice. I have seen some postings with overkill cartridges but I cannot think a better animal to have too much gun for. That being said my cousin has taken 3 large bears with his 30-06, 180 grain nosler partion without event.None ofthe bearsmoved more than 40 yds.