The bullet you use is more important than the caliber/cartridge you shoot.
I’d stick with a Nosler Partition or Accubond, Trophy Bonded Bearclaw or Terminal Ascent (basically same bullet), Remington CoreLokt, Sierra Game King, Swift Scirocco, Northfork Percussion Point or whatever Hornady offers such as an Interlock. Note that I did not say Swift A Frame or Barnes TSX/TTSX. Both of those bullets will certainly do the job and have many times on leopards, but they won’t expand as quickly or large as the bullets I recommended. And rapid expansion combined with decent penetration are what is most important on leopards. They’ll do the job but the others are better choices.
I’ve shot 3 leopards, all on long multi-species hunts so the rifle I used was more general purpose than leopard specific. I shot one leopard, my biggest, with a .300 Winchester and 180 grain Partition. That cat was dead on the limb before he fell. I’ve shot 2 with my .338 Winchester and 225 grain Bearclaws. One was a Kalahari cat on the ground and he didn’t go far at all; maybe 20 yards at the most and the other also was found about 20 yards from the tree I shot him out of. Leopards are not hard to kill as long as you shoot them in the right spot with any of the bullets I’ve mentioned.
If I was going on a dedicated leopard hunt instead of a general bag hunt that includes a leopard, I’d take a 30-06 shooting a 180 grain Nosler Partition. It’s plenty of gun for any leopard.
