For lever action, most of my big cat kills have been 45 Long Colt with a Rossi R92. Beautiful gun, deadly accurate with just its out-of-the-box sights. Some people want to know about light calibers vs mountain lions for defense. Light and heavy calibers are like light and heavy trucks. If you don't have any skill, you usually opt for bigger to make up for it. I have had several mountain lion encounters hunting with my dogs and dispatched 2 170-ish pound cats with my 22LR derringer, only because the rifle was too close to fire. The cats went down immediately with no twitching or nerves. 22 LR right on top of the skull. I carry the little derringer when I'm backpacking for defense. North American Arms. Really nicely made. But I'll never see a cat unless I have my dogs sniffing them out. In the extremely unbelievably rare case you get lucky (or unlucky) enough to even see a cat just hiking, and they, for some reason, want something to do with you (which they don't), just the snap of a little 22LR will tell them that you are nothing to mess with. And in case you DO have to fight a big mountain lion and you are NOT armed, go for their eye sockets. They have very large eyes and they are an extremely exploitable target. I have fended off several cats when the scramble gets going with the dogs treeing one (and they always jump back down) and I am trying to get my dogs to safety just by focusing on damaging the cat's eyes. I'll throw sticks, sand, rocks, rounds, anything at their eyes just to break up the melee and they've winced and backed off. I've also used bear spray and it works but you and the dogs are usually going to get some depending on the wind so I woudn't use that again unless it was just me hiking. On one of those days after bagging the cat and throwing it in the back of my subaru crosstrek, I also helped a few guys who were stuck in their gigantic, heavy, full size dually ford F-WHOKNOWS50 by throwing on the tow strap and using the Subaru's unstoppable All Wheel Drive to pull the massive heavy truck out of the mud. Big and little are easy to navigate. Big brain? You only need a little. Small brain? You see those guys are all over the place and they make up for stupidity with big trucks, big guns, Huge RV's, etc. Be smart. Hunt small. Camp small. Take what you are given, and no more. And you will get another hunt.