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From a Google Search:

Joule = Divide Joule by 1.357 to get ft. lbs.

Zimbabwe
Class A game
Elephant, buffalo, hippo
A minimum bullet diameter of 9.2mm and energy level of 5,300 joules (3,910 ft-lbs) is required. Most outfitters consider the .375 to be a minimum

Class B game
Lion, giraffe, eland
A bullet diameter of at least 7mm (.284) and an energy level of 4,300 joules (3,170 ft-lbs) is necessary.
Most PH's will recommend a .338 mag as minimum on lion

Class C game
Leopard, crocodile, hyena, kudu, sable antelope, blue wildebeest, waterbuck, zebra, nyala, tsessebe, hartebeest, gemsbok, blesbok
A bullet diameter of at least 7mm (.284) and an energy level of 3,000 joules (2,115 ft-lbs) is necessary.

Class D game
Warthog, impala, reedbuck, bushbusk, sitatunga, jackal and animals smaller than 25 kg (56 lbs).
A bullet diameter of at least 5.56mm (.22) and an energy level of 850 joules (630 ft-lbs) is necessary.

South Africa
• Most provinces do not have a minimum equipment requirement for rifle hunting. I typically recommend nothing less than .270 or equivalent
• Some provinces require a minimum of .375 caliber for dangerous or big game hunting.

Mozambique
• There is no minimum equipment requirement for rifle hunting in Mozambique. Like South Africa I would recommend nothing less than .270 or equivalent

Namibia
• Smallest caliber allowed 7 mm (.284).
• Minimum energy (Eo - muzzle velocity)
• Big Game
5400 Joule
(Elephant, Cape Buffalo, Rhino, Lion, etc.)

• Large Game
2700 Joule
(Greater Kudu, Cape Eland, Oryx / Gemsbok, Red Hartebeest, Blue Wildebeest, Black Wildebeest, Hartmann's Zebra, Burchell's Zebra, Giraffe, Sable Antelope, Roan Antelope, Waterbuck, Tsessebe, Leopard, etc.)

• Medium to Small Game
1350 Joule
(Springbok, Impala, Blesbok, Gray Duiker, Steenbok, Ostrich, Caracal, Black-Faced Impala, Red Lechwe, Damara Dik-Dik, Klipspringer, Black-Backed Jackal, Warthog, Cheetah, Nyala, Chacma Baboon, Game Birds, etc.)

Tanzania
• The minimum equipment requirement for rifle hunting in Tanzania is .240 caliber for any game other than dangerous game.
• The minimum equipment requirement for rifle hunting in Tanzania is .375 caliber for dangerous game or big game hunting.

Zambia
• Zambia does not have a minimum equipment requirement for rifle hunting plains game and rely on common sense. Caliber in the .270 range will be well suited for some of the smaller plains game in Zambia.
• The minimum equipment requirement for rifle hunting in Zambia is .300 caliber for dangerous game such as Leopard and Lion. I would recommend .338 for lion as minimum
• The minimum equipment requirement for rifle hunting in Zambia is .375 caliber for dangerous game or big game hunting such as Elephant, Buffalo and Hippo.