 Not finding a cartridge that would fit his needs, he designed a cartridge which he felt would meet his requirements in a dangerous-game cartridge.Jack Lott's original drawings of the cartridge were done on a napkin at a diner.The first cases for the new rifle cartridge were fireformed from .375 H&H Magnum brass into a chamber by using .458 caliber (11.6 mm) bullets which had their bases re-sized so as to fit in the mouth of the .375 H&H Magnum.