300 AAC Blackout (7.62×35mm)

300 AAC Blackout, SAAMI short name 300 BLK, also known as 7.62×35mm is a rifle cartridge developed in the United States and originally chambered in the M4 rifle.

History
Since its inception as the standard US military primary issue rifle ammunition, the 5.56×45mm NATO round has run up against firm opposition from those who argue that the 30 caliber round provides the minimum, if not ideal, performance necessary for the modern battlefield soldier. While 5.56mm NATO has enjoyed widespread acceptance in military circles, the fluid nature of the missions that some special operations groups encounter often demand a round that not only provides better performance than that available in the high energy standard velocity rounds but also one that can offer subsonic performance greater than the current standard 9mm submachine guns now in use.

In an effort to satisfy this need the 300 AAC Blackout was created by Advanced Armament Corp. in cooperation with Remington Defense, under the direction of AAC's Research and Development Director Robert Silvers.

Project goals were:
 * Create a reliable compact 30-cal solution for AR platform
 * Utilize existing inventory magazines while retaining their full capacity
 * Create the optimal platform for sound and flash suppressed fire
 * Create compatible supersonic ammo that matches 7.62×39mm ballistics
 * Provide the ability to penetrate barriers with high-mass projectiles
 * Provide all capabilities in a lightweight, durable, low recoiling package

Meeting these goals allowed the development team to negate many of the perceived drawbacks inherent to other large caliber cartridges when used in the M4 platform. Colt Firearms and other arms makers had previously chambered AR pattern rifles and carbines in various 30 caliber rounds but several issues were encountered. In the case of the 7.62×39mm, its relatively severe case angle caused feeding issues unless specially modified AK47 magazines were used and even then results were less than outstanding. Modified bolts were also needed owing to its larger case head diameter. Rounds such as the 6.8spc and 6.5 Grendel had similar part-interchangeability issues but did allow for the use of the standard M4/M16 30 round magazine albeit with a reduced capacity. Wildcats such as the 300 Whisper and 300-221 addressed these issues but their widespread use in single shot handguns along with the lack of an industry standard cartridge dimension meant that a great number of the popular loads on both the supersonic and subsonic end of the spectrum were less than ideal in the AR pattern weapons. Many of these rounds required an excessively long overall cartridge length that would prohibit feeding in a STANAG magazine while using powder charges that were not compatible with the pressure requirements of the M4 carbine. This was particularly noticeable when using subsonic ammunition in conjunction with a silencer as short stroking and excessive fouling would occur similar to that which was seen in the earliest variants of the M16 in Vietnam.

By keeping the M4 in mind as the primary host during load development the designers were able to work up a host of cartridges that would satisfy not only the ballistic requirements set forth but also ensure mechanical reliability with the fewest changes to the weapon itself, with only a simple barrel change being necessary for a complete conversion.

300 AAC BLACKOUT was approved by SAAMI on January 17, 2011.

On October 23, 2011, SSG Daniel Horner of the USAMU used 300 AAC Blackout to win his 4th USPSA Multi-Gun National Championship.

Performance


Maximum effective range = *460 m 125 grain supersonic
 * 200 m 220 grain subsonic

Predecessors
The 300 AAC Blackout is a SAAMI standardized 300-221. Hornady states that any rifle chambered for the 300 AAC Blackout can shoot their 300 Whisper ammunition, which is made to within 300 AAC Blackout specs. The reloading dies for these two cartridges are often the same.
 * Pioneering work by the USAF Armament Lab at Eglin Air Force Base in the late 1960s produced the 7.62×28 cartridge which propelled a 172gr match projectile to the 1050 ft/s range but suffered from various reliability issues.
 * More recently, popular wildcats such the 300-221, 300 Fireball, and JD Jones' proprietary version of them, the .300 Whisper, have furthered the concept.