Most folks don’t ever plan on running into a mountain lion, but if you spend time in the backcountry, it’s a possibility you can’t ignore. If one decides to charge, you don’t get time for second guesses. That means your choice of caliber matters a lot more than people think. Some rounds just aren’t up to the task—and carrying the wrong one can get you hurt, or worse. Let’s talk about what not to trust when things go sideways.
.22 LR
It’s no surprise that the .22 LR makes this list. It’s a fun plinking round and decent for small game, but a charging cougar? Not a chance. Even with a perfect shot, the lack of penetration and stopping power leaves way too much to chance.
Some people argue that shot placement matters most—and sure, it does. But when adrenaline’s pumping and that cat is closing in fast, the .22 just doesn’t cut it. You need a round that hits harder and breaks bones.
.25 ACP
The .25 ACP might be easy to carry, but it’s not going to stop anything with claws and fangs. It barely outperforms the .22 LR and is often used in small pocket pistols that aren’t made for serious defense.
Even if you emptied a mag into a mountain lion, it might not be enough to slow it down before it’s on top of you. That’s a bad tradeoff. Stick to something with a little more muscle behind it.
.32 ACP
There’s a reason you don’t see many folks recommending the .32 ACP for wilderness carry. It’s soft-shooting, but that low recoil comes at the cost of penetration and expansion—two things you desperately need against a wild animal.
If you’re relying on this round to stop a full-grown mountain lion, you’re gambling with your safety. It just doesn’t have the punch to guarantee a quick stop, even if you’re calm under pressure.
.380 ACP
This one might stir the pot. Yes, the .380 ACP is a step up from the mouse guns, and some people swear by it for self-defense. But when it comes to animals, especially something as fast and strong as a mountain lion, it’s borderline.
Penetration is still limited, and expansion can be spotty depending on the load. In a pinch, it’s better than nothing—but there are much better options out there for backcountry carry.
.22 Magnum
The .22 Magnum gives you more zip than the .22 LR, but not enough to rely on it in a life-or-death encounter with a predator. It’s great for varmints and maybe foxes—but a 150-pound cat is a different story.
Sure, it’s light and low recoil, but that doesn’t help when you need immediate stopping power. Don’t let the higher velocity fool you—this round isn’t meant for serious defense against wild animals.
5.7x28mm
The 5.7x28mm is fast and flat-shooting, and it’s got a loyal fan base. But while it can penetrate soft armor, it’s not particularly effective against bone or heavy muscle. Mountain lions have both.
It’s a high-velocity round, but it was designed more for defeating barriers and armor, not for delivering heavy terminal energy. Against a predator in full sprint, you’ll want something that hits a lot harder.
.17 HMR
The .17 HMR is a varmint round—fast, accurate, and great for squirrels or prairie dogs. But it’s just too light for anything bigger. The bullets fragment easily, and that’s not what you want when deep penetration counts.
It might impress on paper, but in real-world use, it simply won’t do the job against something that can cover 20 feet in a single leap.
.410 Bore (Handgun)
A .410 out of a handgun might look intimidating, but in practice, it underdelivers. Most loads meant for defense don’t penetrate deep enough, and the spread isn’t tight enough to guarantee hits under pressure.
It’s better suited for snakes and small pests. Against a mountain lion, it’s not going to deliver the kind of immediate stop you need when things go bad.
9mm with FMJ
The 9mm itself isn’t a bad round, but if you’re carrying FMJ in the woods, you’re not doing yourself any favors. Full metal jackets zip through without transferring much energy—something you can’t afford when trying to stop a charging animal.
If you insist on 9mm, at least go with a heavy-duty hollow point that’s proven to expand and penetrate. Otherwise, you’re likely to poke holes without stopping the threat.
Birdshot (Any Gauge)
Birdshot is made for—you guessed it—birds. It spreads fast and doesn’t penetrate deeply, which is exactly why it’s useless for anything bigger than a rabbit. People sometimes carry it in shotguns for snakes, but it won’t help against a cougar.
If a mountain lion is closing the gap, birdshot’s going to make it mad, not dead. You need buckshot or slugs—nothing less.
*This article was developed with AI-powered tools and has been carefully reviewed by our editors.
