A completely new cartridge needed to be designed and the 300 Whisper, pioneered by JD Jones, was picked because the guardian case. Considering that the 300 Whisper was a wildcat cartridge, and thus couldn't simply just be adopted for navy use since it wasn't SAAMI standardized. The very last thing https://armsandsammo.com/product-category/rifle-ammo/350-legend-ammo/