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 by Advanced Armament Corporation (AAC) for use in the M4 carbine. Its purpose is to achieve ballistics similar to the 7.62×39mm Soviet cartridge in an AR-15 platform while using standard AR-15 magazines at their normal capacity.

History

While 5.56×45mm NATO has enjoyed widespread acceptance in military circles, the nature of the missions encountered by some special operations groups often demand a round that not only provides better performance than that available in the high-energy standard velocity rounds, but one that can offer subsonic performance greater than the current standard 9mm Luger round.^[1]

In an effort to satisfy this need the 300 AAC Blackout was created by Advanced Armament Corporation in cooperation with Remington Defense, under the direction of AAC's Research and Development Director Robert Silvers and with the support of the company's founder, Kevin Brittingham.^[2][3]

The project's goals were:

• Create a reliable compact .30-cal solution for AR platform
• Use 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 shorter, lightweight, durable, and 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.^[4] Modified bolts were also needed owing to its larger case head diameter. Rounds such as the 6.8 SPC 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.^[5]

300 AAC Blackout rounds shot from a suppressed M4 Carbine.

Wildcat cartridges such as the .300 Whisper series 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 suppressor as short stroking and excessive fouling would occur similar to that which was seen in the earliest variants of the M16 in Vietnam.^[6]

By keeping the M4/M16 platform 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.^[7]

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.^[8]

Performance

Example of a 300 AAC Blackout shot in a block of gel.

Maximum effective range = *460 metres (503 yd) 125 grain supersonic

• 200 metres (219 yd) 220 grain subsonic

The 300 AAC Blackout was designed to achieve energies similar to the 7.62×39mm Soviet in an AR-15 platform while using standard AR magazines at their full capacity. The 7.62 Soviet's cartridge taper prevented reliable feeding in AR magazines and created wear on the bolt. From the 14.5 in (370 mm) of the M4 Carbine, the M855 5.56 mm round has an effective point target range of 500 meters. The bullet has significant drop, drift, and energy loss at that distance. From a 16 in (410 mm) barrel, a 125 gr (8.1 g) 300 BLK round has a lower velocity and similar bullet drop and drift at shorter distances. However, it has the same amount of energy at 700 meters that the M855 has at 500 meters. In terms of hit probability, the Blackout has an effective range of 460 meters. From a 9 in (230 mm) barrel, the 125 gr BLK round has the same muzzle energy as the M855 from the M4, and 5 percent more energy at 440 meters. In comparison with 7.62×39mm rounds, 300 BLK rounds with varying loads have a better ballistic coefficient and more energy out of similar length barrels. 300 BLK rounds have "barrier blind" performance, being capable of penetration through several inches of different hard targets. The .30 caliber cartridge has an 89.1 percent increase in frontal bullet area over the 5.56 mm, and so leaves a large wound cavity in soft targets. It also penetrates deeper and initially yaws faster. 300 BLK rounds are effective out of barrels as short as 4.5 in (110 mm). Weapons chambered for the round can be as light, compact, and quiet when suppressed as submachine guns like the 9 mm Parabellum MP5 and 4.6×30mm MP7 while having more energy and accuracy at longer range.^[9][10]

Compared to the 6.8×43mm Special Purpose Cartridge, another round made to have increased stopping power over the 5.56 NATO, the 300 Blackout has different capabilities. The 300 BLK was designed with a specific shorter-range focus to have equal or more energy than the 7.62 Soviet and work reliably with suppressors. The earlier 6.8 SPC was simply designed to have more energy at all ranges than the 5.56 mm. It has a relatively small projectile with a high velocity that maintains performance at range. At 200 yd (183 m), the 300 BLK drops 2 in (51 mm) lower than the 6.8 SPC, while it drops 30 in (760 mm) lower at 500 yd (457 m). The 115 gr (7.5 g) 6.8 round has a higher muzzle energy of 1,694 ft·lb (2,297 J) due to its greater velocity, while the 125 gr (8.1 g) 300 BLK round has a muzzle energy of 1,360 ft·lb (1,840 J). Both rounds were made to be used in an easily converted AR-15 platform. The 6.8 SPC has a more difficult conversion because it was designed around the .30 Remington cartridge, requiring a different bolt and decreasing standard magazine capacity. The 300 BLK was made specifically for ease of conversion, so the standard bolt will work and a magazine can be used to its full capacity, so the only change needed is the barrel.^[11]

Extreme care should be taken with 300 BLK ammo, as with certain bullet profiles, the round may chamber in a standard .223 or 5.56 AR platform with disastrous results and possible injuries. ^[12]

Predecessors

• 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 1,050 ft/s (320 m/s) range but suffered from various reliability issues.^[13]
• More recently, popular wildcats such the .300-221, .300 Fireball, and JD Jones' proprietary version of them, the .300 Whisper, have furthered the concept.^[14]

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 within 300 AAC Blackout specs. The reloading dies for these two cartridges are often the same.^[15]

See also

• .300 Whisper
• 7.62x37mm Musang
• 7.62×40 Wilson Tactical
• List of rifle cartridges
• Table of handgun and rifle cartridges

References

External links

Wikimedia Commons has media related to 300 AAC Blackout.

• Official website
• SAAMI drawing