Twelve gauge slugs or standard buckshot are pretty much all you need for dealing with wolves. Bears, though, could be put down with something like a .30-06 rifle, such as the 1903 Springfield, but there are more reliable - and more expensive - means.
Anything in .458 Winchester could do, though you'll probably give yourself some major bruising if you're not prepared. And, of course, there's the lung-collapsing hilarity of .500 S&W. Just make sure to get that in a lever action rifle platform or something, like so.
![](https://www.bighornarmory.com/wp-content/uploads/2018/06/model-89-carbine.jpg)
Oh, and no, there are no hunting grenade launchers. For one, you'd be picking bits of game out of the trees, and two, the cops would be wondering why in the lemon fresh *fuck* someone's lighting off explosives in the woods.
Source: My dad's an experienced game hunter. Mostly deer, but he did go to Zimbabwe once and bagged a water buffalo.