I've never hunted grizzly bear and probably never will unless I hit the lottery and someone develops a miracle drug that will repair my injured back and legs. I do however black bear hunt and carry enough gun to get the job done; 35 Whelen or .358 Winchester. If I were to go grizzly hunting I'd be carrying nothing less than a .338WinMag or one of the .375 guide guns, or something along that line for the hunt. And.....I am smart enough and do learn from others.
Now I get a bit riled up when I read all about the 6.5's with bullets that are promising or show promise! I'd like to suggest that instead of asking a forum that is all about Long Range Hunting, perhaps you might want to go ask some of hunters who have been mauled or injured by a grizzly bear instead!
I live in a little, small town in Rhode Island, so what would a small town ole guy know about bear hunting. There is a group here in town and that goes to Alaska every year; a drop camp where they stay for a week or two. I hunt and shoot all of the time and was curious about what caliber rifle to hunt grizzly. I saw one of the hunters and asked what he was hunting grizzly with. The hunter told me that he was using a .300WinMag.. My next question was, "Isn't that a little light for grizzly?" The reply was, "Oh no that's more than enough to drop a grizzly, my father has been using one for years!" Many years later we heard that one of the hunters had been mauled by a grizzly and he was in serious condition in an Alaskan hospital. Remember this is a small town, the hunters were all respected members of our community. Months after his injuries I was able to speak with the hunter. He told me that after shooting the grizzly, he waited about 90 minutes and he and the group he was hunting started tracking the bear. He said that all of a sudden the bear charged at him from the alders, he was able to get one shot off at close range and when he attempted to load another round his rifle jammed, the bear was upon him and bit the end of his barrel tearing the rifle from his hands. The mauling went on for some time during which he was mauled on his stomach, buttocks and head. The other hunters were afraid to shoot the bear while it was attacking because they feared hitting him. The hunter was in a tent being attended by his companions for three days because the weather prevented any kind of rescue. Eventually he was liter carried 3 miles over tough terrain to a helicopter.
The rifle that the hunter was using was a very accurate, Browning in .300WinMag. When the hunter tried to reload for the second shot, he tugged so hard on the bolt that the extractor failed, and it ripped through the base of the casing. That left a chamber with a fired round in it, the next round jammed up between the spent casing, magazine follower and the bolt. Now when the hunters go up for their annual hunt, all four hunters are carrying controlled feed, ".338 Winchesters". Oh and the hunter went back the next year to the area where the incident took place and found the remains of the bear that had mauled him. When I asked him how he knew that it was the same bear, he said he knew because the teeth marks matched those in his head; and, he does have two large scars there to prove it. My thoughts on a handgun are that I'd rather rely on my rifle to get the job, and that if I am into my handgun then I am in real trouble. And....I always do carry a Glock20, 10mm when bear hunting.
So if the OP wants to take the 6.5 with bullets that have promise have at it; however I suggest that he talks with someone who has actually been there and done it before making a choice. Personally I'd rather be carrying something that I was confident in than asking myself, when the ---t hits the fan, if I was carrying enough gun to get the job done!!