Roy Weatherby had expected the .378 Weatherby Magnum to make some headway in the African continent but believed that his cartridge was being bypassed for low-velocity, big-bore cartridges by professional hunters who he felt were resistant to change. Furthermore, new regulations prohibiting the hunting of heavy, thick skinned, dangerous game with sub-.40 caliber (10.16 mm) cartridges were being enacted in some African countries. These regulations would essentially ban the use of all previous Weatherby cartridges for the hunting of elephant, African Cape buffalo and rhinoceros.