No personal experience, but I've heard two things about moose. They're not exceptionally hard to kill, but it can take awhile for them to realize they're dead. I've read of them absorbing killing shots from 375 H&H and 458 Magnum rifles and continuing to wander about and eat until they fall down. Your 450 load seems like it should've been deadly, but animals are funny sometimes. Whether an expanding bullet is right for Brown bear is something I cannot speak to, but it seems the classic stories I've read about hunting them with handguns tends to involve heavy HC lead. But, bullets are also much better now than when Larry Kelly and JD Jones were pioneering the sport of taking really big game with handguns. That's a long way to say, I don't know, but good luck and be careful!
But for the grace of God, there, I go.