The .300 Whisper (7.82x34mm) is a CIP standard 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 at subsonic velocities.
The .300 Whisper, displayed center.
The .300 AAC Blackout, also known as 7.62×35mm, is an intermediate cartridge developed in the United States by Advanced Armament Corporation (AAC) for use in the M4 carbine. The cartridge yields increased performance in shorter barrels and effective subsonic performance for silencer use when compared to 5.56mm NATO. The .300 AAC Blackout uses standard 5.56mm NATO magazines and components with the exception of the barrel.
The .300 AAC Blackout plastic tipped, left, compared to .300 AAC Blackout 125 gr match, .300 AAC Blackout 220 gr subsonic, 5.56×45mm NATO, and 7.62×39mm.
.300 AAC Blackout rounds shot from a suppressed M4 carbine
Example of a .300 AAC Blackout shot in a block of gel
AR-15 rifle with dustcover and magazine band that identify it as having a chambering of .300 AAC Blackout