I have killed several blackies. And just about any rifle with a well placed shot will do. With your rifle the heavier the bullet the better. However, I shot a six footer last year with my Rem. 6mm at 55 yds. And he dropped in his tracks. When I go back to alaska I am going to buy a Marlin 444. Or something similar to that. You know what they say, Bigger is Better. And you didn't mention, but if you are hunting with a guide some of them require a minimum caliber. So check with them. Hope your season goes well. If there are any other questions I can help you with just give me a shout.