Agree with those who suggest .30 caliber or better..if you are hunting larger game and using a .375 H&H ..that would be fine as well..but, after having shot various cats in Africa, dont think you would need anything more that a 30-06 with a good quality bullet--say 180 A-Frame..your shots will not be that far.and it offers plenty of power for a leopard..any of the .300's would also work great as well..300 win or weatherby mag...

As earlier stated, shot placement is parmount, so if you feel the .416 is a mule,,,would NOT use that ..you need to be dead on for the shot..and if you are, the rest will sort itself out..

BTW--I have 2 custom rifles for the .257 weatherby--one of my favorite calibers for use here in Montana for deer and antelope..incredible round..but would still not be my choice for a leopard..

Ripp