The .270 would be ok on a cougar, just remember that even though a cougar is big, they are fairly delicate and light boned creatures . Personally I would opt for something a little lighter, because when your predator calling you never know what might come sneeking in. If you have a coyote come in, which is more than likely to happen, or even a bobcat, the .270 would destroy the pelts on both of those, which in the winter time can fetch you some good money. I personally hunt with a rifle chambered in .223, but where I hunt we dont get severley harsh winters, and the coyotes and cats dont seem to get as thick a hide on them. So for hunting them in an area like Idaho that has cold winters, you might opt for a .243

What if I ran a really light bullet through the .270, maybe 85 or 100 grains? would this still be too much?

If you are concerned about hide damage on a predator use solid bullets,a 270 loaded with a solid bullet will not damage the pelt any more than a .223 would.

That is a true point. I have destroyed a few pelts with the .223, most of those were from hollow points that hit bone, either in the rib cage or shoulder blades.

Thanks for the suggestion, I had totally spaced the idea of using solid bullets as I usually am hunting elk and mulies where I always use soft, expanding bullets.

I have seen alot of kills on mountain lions, and I agree that a 223 is ideal. I like a ballistic tip bullet, they usually make an entrance, and no exit. The bullet disintegrates inside for a quick kill, and minimal pelt damage. The larger calibers work fine with solids, of heavy constructed bullets for large game, usually they don't expand at that close of a distance. They all work fine, whatever you have will work. (but the 223 is my favorite),
L. Sorenson

just a predator call is what you use athough you will probably call coyotes and lions but coyotes are fun to shot also.