.300 Whisper / .300 AAC Blackout (7.62×35)

.300 Whisper

The .300 Whisper cartridge was originally developed in 1992 by J.D.Jones of SSK Industries (USA). It was a member of a family of wildcat / proprietary rounds, optimized for subsonic performance.

This round was based on the .221 Fireball case, necked up to accept .308 caliber (7.62mm) bullets. .300 Whisper can accept heavy bullets up to 220 grains (14.3 grams), while maintaining an overall length compatible with 5.56×45 / .223 Remington actions and magazines. It also shares the same case base dimensions with .223 / 5.56, allowing for simple conversions (by changing the barrel) of existing 5.56mm / .223 weapons to fire .300 Whisper.

Over recent years, several major ammunition manufacturers in the USA and Europe began to load this caliber commercially. It has been offered to both civilian and government (LE and military) users, in subsonic as well as supersonic versions.

The .300 Whisper cartridge is certified by the European CIP commission, making it a ‘standard’ round across most of Europe and in many other countries that recognize CIP certification.

When loaded with heavy subsonic bullets, .300 Whisper outperforms most (if not all) subsonic pistol / submachine gun cartridges in terms of accuracy and effective range. It allows for effective target engagement at ranges of up to 150-200 meters. With relatively light supersonic loads .300 Whisper is a close match to the venerable Russian 7.62x39mm M43 warhorse, making it an effective 400-meter infantry cartridge. It can also  be used for target shooting and for short-range hunting.

The .300 AAC Blackout was developed in 2009-2010 upon requests from US Special Operations forces to the US-based company AAC. It was intended as a dedicated subsonic ammunition for suppressed shooting out of modified 5.56×45 / .223 Rem weapons. The best starting point for such a round was the .300 Whisper cartridge described above. Since the original customers require SAAMI certification, which is impossible with trademarked rounds (which of course .300 Whisper is), AAC developed their own version of the necked-up .221 Fireball case which would accept 7.62mm / .308 bullets of various weights.

.300 AAC Blackout is externally and ballistically similar to its parent .300 Whisper round, and in many cases these two are considered interchangeable, but it is still recommended to use only ammunition types which are specified for any given firearm by its manufacturer.

Today many US manufacturers load .300 AAC commercially, with both subsonic and supersonic loads. Many existing 5.56mm / .223 Rem weapons can be easily converted to .300 AAC just by changing the barrel.

An inherent and serious drawback of this family of cartridges results directly from one of its major advantages, that is, compatibility with 5.56/.223 bolts and magazines. As a result of this, the .300 AAC or BLK round can be inadvertedly chambered into a 5.56mm/.223 rifle, with catastrophic results.



Bullet weight, g Muzzle velocity, m/s Muzzle energy, J Comments

.300 Whisper 208 gr A-MAX

13.5 311


Subsonic load by Hornady
.300 Whisper 220 gr SWISS P FINAL




Subsonic load by RUAG
.300 Whisper 110 gr V-MAX




Supersonic  load by Hornady

.300 Whisper 130 gr SWISS P BALL

8.4 650


Supersonic  load by RUAG
.300 AAC 220 gr MatchKing BTHP




Subsonic load by Remington
.300 AAC 125 gr AccuTipBT




Supersonic load by Remington