No large Caliber is needed for Leopard. The Minimum in Zim is a .270 . The minimum in Namibia is rated in Joules. So a 6.5 Mag is acceptable but the APHA recommend a 7mm Mag minimum..I have yet to see a PH backing up for dangerous game using a scope. There is some good info at Pro Safaris (
https://www.pro-saf.com/) It used to be owned by Norman Crooks but he sold it to his Kids. I know Norman personally and the only Person that has taken more cats them him is the Man that taught him. I believe Norman told me he has harvested around 220 Leopards. He is know in Africa as The Cat Man.
