7.62×35mm

7.62×35mm / 300 AAC Blackout
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.
Type	Rifle
Place of origin	United States
Specifications
Parent case	221 Fireball/.223 Rem
Case type	Rimless, Bottleneck
Bullet diameter	0.308 in (7.8 mm)
Neck diameter	0.334 in (8.5 mm)
Base diameter	0.376 in (9.6 mm)
Rim diameter	0.378 in (9.6 mm)
Case length	1.368 in (34.7 mm)
Overall length	2.26 in (57 mm)
Rifling twist	1:7
Primer type	Small rifle
Maximum pressure (SAAMI)	55,000 psi (380 MPa)
Maximum pressure (CIP)	62,366 psi (430.00 MPa)
Maximum CUP	52000 CUP
Ballistic performance
Bullet mass/type Velocity Energy 125 gr (8 g) OTM 2,215 ft/s (675 m/s) 1,360 ft·lbf (1,840 J) 220 gr (14 g) OTM 1,010 ft/s (310 m/s) 498 ft·lbf (675 J) 78 gr (5 g) Lehigh Defense CQ 2,800 ft/s (850 m/s) 1,358 ft·lbf (1,841 J) 90 gr (6 g) Barnes OTFB 2,550 ft/s (780 m/s) 1,300 ft·lbf (1,800 J)
Test barrel length: 16 in Source(s): Official website

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 while using standard AR-15 magazines at their normal capacity. Care should be taken not to use 300 BLK ammunition in a rifle chambered for .223/ 5.56 or 7.62×40mm Wilson Tactical (see section on misuse).

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 provides better performance than that available in the high-energy standard velocity rounds and subsonic performance greater than standard 9mm (the ubiquitous pistol round also commonly used in many SMGs).

In an effort to satisfy this need, the 300 AAC Blackout was developed. It can be seen as a SAAMI-certified version of Jones' Wildcat .300 Whisper. 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.

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. 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 AK-47 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 6.8 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.