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 Remington
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	1-8″ (203 mm)
Primer type	Small rifle
Maximum pressure (SAAMI)	55,000
Maximum pressure (CIP)	56,565
Maximum CUP	52,000 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) 110 gr (7 g) Hornady Black V-MAX 2,375 ft/s (724 m/s) 1,377 ft⋅lbf (1,867 J)
Test barrel length: 16 in

The .300 AAC Blackout (designated as the 300 BLK by the SAAMI and 300 AAC Blackout by the C.I.P.), also known as 7.62×35mm, is an intermediate 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 cartridge or, even more similarly, the 7.92×33mm Kurz cartridge in an M4 while using standard M4 magazines at their normal capacities. Ammunition in .300 BLK cannot be used in a rifle chambered for 7.62×40mm Wilson Tactical. It is mainly derived from the .300 Whisper concept, but differs in having been submitted to the SAAMI.