It occured to me that if I'm going to have this wild and wooly North American Pleistocene megafauna, that folks who wander the wilderness may need to have very high caliber rifles to stop charging bison bulls, or elephants or other big, mean animals that can take half a dozen "lesser" bullets and keep on moving. Elephant guns, as they're called. I didn't really give much thought to what it would be like to fire an elephant gun, though.
Here's a few youtube clips of some guys in a range firing the .577 Tyrannosaur cartridge. 220 lbs of recoil force. Holy smokes.