300 Whisper Ammo
The .300 Whisper is a wildcat cartridge in the Whisper family, a group of cartridges developed in the early 1990s by J.D. Jones of SSK Industries. It was developed as a multi-purpose cartridge, capable of utilizing relatively lightweight bullets at supersonic velocities as well as heavier bullets (200–250 grains) at subsonic velocities.
.300 Whisper is also sometimes known as .300 Fireball or .300-221, but there is some variation in dimensions and pressure between these cartridges. Some implementations of .300 Whisper meet the SAAMI specifications for 300 AAC Blackout.