Leopards are small animals by dangerous game standards. I would recommend a good deer rifle and bullet combination over a large bore any day. There isn't a .416 bullet that will open up one micron when it hits the pelvis of a leopard, let alone the rib cage. A 150 - 180 grain pill at 3000fps would be my choice for a leopard slayer. The shock of a high velocity round opening up is well known. The trauma caused by these high velocity pills is greater that that of a large bore. Just my .02$. Good luck on your hunt.