 It was similar to the reasoning behind the shortened cases used by Weatherby as DuPont's IMR 4350 was the slowest burning powder available then.The .264 Winchester Magnum is a cartridge which was standardized by SAAMI, which published recommended specifications for the cartridge.SAAMI recommends a six groove barrel with a rate of twist of one revolution in , a bore diameter of and a groove diameter of with each groove having a width of .