This is not a simple question as you might think. Africa is not a country it's a continent. there are 63 countries on that chunk of land. Each has it's own laws and policies.
When you decide to book a hunt you should make certain that the outfitter and/or PH you arrange it with provide you with minimum cartridge laws. In most countries I know of a 338 would be fine, but the laws change so fast and are different in each country that it's not possible to make a statement like this "in general" without exact data of the hunt.
It's sounds like you only testing the water otherwise you would have asked the PH or outfitter already, ........That is my guess. If you want a best "guess" idea let us know where you will hunt, and I can give you an Idea. I doubt that any PH would blink an eye in the use of a 338 for a leopard. After all they weigh less then 200 pounds and are usually shot under 50 yards. For my hunters the more important tool is a great scope for low light.
