The 300 Whisper was designed for the purpose of firing extremely heavy, accurate, ballistically efficient bullets at sub-sonic velocities and is now the state of the art long range cartridge in suppressed weapons. It delivers more energy more accurately than any existing sub-sonic round at 200 yards (and a lot further, except other Whispers). In addition, it has interesting sonic capabilities - possessing greater versatility than any other cartridge capable of performing in these vastly differing arenas. 

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