I too, agree with most that has been said. The thing is, with a question like this one, alot of different calibers will "kill" if placed in the correct spot and the bullet holds together. This can be from a 100gr .243 to a 700gr .600NE. Yes, the .257 Weatherby Will kill a leopard. Is it the best caliber for this task? No. Why? Velocities are too high and the bullet is too light. I think the best answer to most questions about "is this or that caliber good to use on specific game", two things need to be addressed. 1) What is the minimum grain bullet that I should use for the task? 2) What type bullet should I use? In answering #1, to me (and this is just my humble opinion) the minimum on leopard should be 160gr. This will put you into the .284 - .308 diameter catagory as a minimum. .7mm Rem. Mag, 30-06, .300WSM, 300Win. Mag, etc.. any, and all of these will work perfectly. Getting into the big dia. calibers, bleeds over into the next question - bullet construction. Most bullets in the bigger calibers are designed for penetration in heavy muscle mass and bone. (Not needed in a thin skinned leopard) You are looking for hydrostatic shock with bullet expansion & weight retention. These are readily available with, you pick, Swift A-Frame, Nosler Partion, Nosler Accubond, Federal Fusion, etc.... In dealing with the most feared animal on the planet to follow up wounded, why take a chance with your choice of weapon? Other factors will be coming into play at the time of pulling the trigger, without doubting your choice of weapon. Lighting, nerves, excitement, adrinaline. Walking up to that bait tree after the shot, hoping for a dead leopard.....that .257 will really seem really, really small.