Ballistically speaking, it's about a power twin to the 357 mag out of a rifle, and much less than the old 30/30. Matched with properly with bullets that expand at the slow velocities it does ok under 100 yards under ideal conditions for medium game; just like the 357 mag. I've taken three black-tails with it when we had permission to carry the round in our patrol cars. It was later dropped as a patrol rifle round due to it's inability to penetrate even low rated body armor.
There are a whole lot better choices for big game in the SUR (sport utility rifle) platform than the 300 whisper for hunting in the Pacific Northwest from 6.5 Grendel to the 308/223, 450 Bushmaster and any of the WSSM based cartridges. What you don't want to be is under powered should you get a nice shot at a big bear or buck.
Just my .02 of experience.