The 338-378 KT was designed by Elmer Keith and Bob Thompson in the 1960’s as a long range elk cartridge to be used with slower burning powders available at that time. They kept the Weatherby double radius shoulder but shortened the case 1/4″ to better suit case capacity to the burn rate of the slower burning powders. Performance mirrors the modern 338 Rem Ultra Mag. The 338-378 Weatherby is based on the 338-378 KT.