The Whisper family was developed as a line of accurate, multi-purpose cartridges using relatively heavy rifle bullets for a given caliber in subsonic loads.
[1][2][3] The intention was to create an extremely accurate cartridge family for military, police, competition and specialized hunting markets that could also be easily sound suppressed.
While all cartridges in the Whisper family must be capable of accuracy using subsonic loads, most of the smaller caliber cartridges of the family (.308" and under) are also capable of being loaded to supersonic velocities using relatively lightweight bullets for their caliber, increasing their utility.
Additionally, in some cases, subsonic loads are often intended to avoid the turbulent transonic zone entirely, maximizing potential accuracy.
Like the rest of the Whisper Family, these two cartridges are designed to fire rifle bullets at subsonic velocities.