The nut behind the bolt makes a big difference. You're using a good penetrating bullet so as long as you can make a good shot it should be fine. IMO it's important to take out BOTH lungs on a bear. Even a deer can go a long way with a one lung hit. Having spent a good amount of time in a Maine bear camp I've seen several non-recovered with hits from 270s.... but there's lots of variables. The guide there will no longer guide hunters with less than a 28 caliber shooting at least a 170 grain bullet. Quite a few lost with bow hits also. Take from that what you will. I do not think a 270 is plenty, but it should do the job with the bullet you're using and a double lung hit.