Another Weatherby wildcat, first introduced in the 1960s. It started out as the 338-378 Keith/Thompson, a pure wildcat developed my Mr. Thompson and Elmer Keith. It is based on the 378 Weatherby case shortened to 2.5 inches. This is the ultimate cartridge for long-range, big game hunting. Delivers more than 5,000 foot pounds of energy at the muzzle with a .338-sized bullet. Extremely powerful and flat-shooting. Based upon the .378 case, necked down to .338. Reintroduced as a Weatherby production cartridge in 1998. 

This text is based on information from “Cartridges of the World”, Hodgdon reloading manual, the cartridge designer and/or own resources.