If you were to go hunting mountain lion with a 357 mag lever action. What would be your load?
Factory or reloaded ammo?

I'd probably load a heavy, hard-cast, wide-meplat bullet for penetrating from any angle.

I would go with 158gr JHP Remington. If you are hunting with hounds the JHP will work just fine. You'll have the time to place the shot and it's usually side to side or bottom to top body shot.

DITTO, 158 NOSLER OR GOLD DOT SPEER DRIVE IT ABOUT 1600 .BLUE DOT OR 2400 WILL DO NICELY.
WOULD MAKE A CAT VERY VERY SICK

I would guess a lot of loads would actually work out ok. Here in Idaho a lot of the cats are shot with .22Mags out of the trees.

My deer load was 158 RP JSP Lil Gun 2050 fps in a Marlin. I'd be happy w/that. Bud shot his w/a 9mm not long ago......plenty power hear.

I'd expect the JSP to penetrate a tad more than a JHP, though broadside lungs, the HP wouldn't be a bad thing.