Blood tracking bears

[scree]

I don't know there is a for sure answer.  I know that bears are tough and the fat and hair can make things complex in a hurry.  I have killed 4 bears.  2 with a rifle and 2 with a bow (and I lost a 3rd with a bow; still don't know how that happened). Both with a rifle were close and DRT. Both with a bow were near perfect shots and they both went about 50-60 yds.  One had a good blood trail the other one only left a drop of blood and some hair at the shot sight. 
With a rifle, breaking the shoulder makes a lot of sense to me.  Bullet construction has come a very long way in the last few years and can make a substantial difference.  That is not to say that shot placement is not even more important but it all factors in.  I guess my thoughts are a larger caliber rifle with a premium bullet are not sure fire but certainly would help.

[Crunch14]

Headshot5 and h20hunter: Do you think a 180 grain nosler partion bullet from a 308 is good for breaking bone or should I consider a different bullet?

I use those in my .30-06 as well as my Dad.  They are awesome.  We've never had an animal take more than a few steps.  Bear, Elk, Deer all have dropped pretty much in place.