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 carbine . 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 Corporation in cooperation with Remington Defense , under the direction of AAC ' s Founder , President , and Head of Engineering , Kevin Brittingham . Project goals were : 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 suppressor 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 / 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 . 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 = * " 125 grain supersonic " 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 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 barrel , a . 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 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 . 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 . 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 .