600 lb Mama and (2) 400 lb cubs(?) - Sounds VERY big to me. I'm sure when a couple of them are trying to eat you...they probably look much bigger. I just saw a picture of a 700 lb. Michigan bear that got ran over with a combine last week - so they do get that big up there.
Story like this makes me remember why I carry a .41 mag even when bowhunting. By the way - I think I would have tried to shiskabob (sp?) him with a broadhead instead of throwing my bow at him to scare him away. Hindsight is always 20/20.
