The best advice is read this: http://forums.accuratereloading.com/eve/forums/a/tpc/f/4711043/m/2861098911

One thing to remember if you do need to shoot a lion it's going to be just you and the loin. Not you the loin and your PH with more than likely a double big bore rifle to back you up, if things go bad.

My advice would to find a 458 WM Winchester Model 70 CRF cut the barrel to 20" and load it with some CEB 258 GR. bullets. Remember it's not just the caliber of a gun but the bullet it delivers.

https://cuttingedgebullets.com/cgi-bin/commerce.cgi?preadd=action&key=FB_S258_RAPTOR