I have to agree that the best single purpose survival gun is my 870 with the short barrel. Stuff it down the side of a pack with slugs ready to go and a bunch of bird shot packed away and you're ready for predators and to be a predator.
The 45-70 is my helicopter gun. When we get to a place that has the potential for bear I bring it out, load it and it's just there to make me feel good. I've never shot it in anger or fear. I will say that it has a cool factor that I just love
It's just such a bad ass cowboy donkey puncher.