What is 8.6 Blackout? 8.6 Blackout (8.6 BLK) is a .338-caliber rifle cartridge made from the 6.5 Creedmoor case, shortened and necked up to hold .338-inch bullets. It fires heavy subsonic bullets of roughly 300 to 350 gr for suppressed shooting and lighter supersonic bullets around 200 gr, from short barrels. SAAMI published its standard for the cartridge in January 2026. Chattahoochee Munitions manufactures complete 8.6 Blackout firearms on the CM7S bolt action and the CM10 AR10.
What Is 8.6 Blackout in One Paragraph?
8.6 Blackout is a short, fat .338 cartridge in the .308 Winchester family. Because it keeps the 6.5 Creedmoor case head, it uses a standard .308 bolt face and fits .308 and 6.5 Creedmoor length magazines. Changing a short action or AR10 to 8.6 Blackout is mostly a barrel change. What sets the 8.6 Blackout apart is very fast rifling, 1:3 to 1:6, which lets long, heavy subsonic bullets stay stable at about 1,000 fps.
What Is 8.6 Blackout Made Of? Specifications
| Specification | 8.6 Blackout |
|---|---|
| Bullet diameter | .338 inch (8.6 mm) |
| Parent case | 6.5 Creedmoor, shortened and necked up (.308 Winchester family) |
| Case length | 1.685 inch |
| Cartridge overall length | 2.560 to 2.810 inch |
| Bolt face | Standard .308 Winchester |
| SAAMI maximum average pressure | 62,000 psi |
| SAAMI reference velocity | 200 gr at 2,200 fps (16-inch test barrel) |
| SAAMI test barrel twist | 1:6 |
| Typical subsonic bullets | 300 to 352 gr, about 950 to 1,050 fps |
| Platforms | AR10 and short-action bolt action |
Pressure, reference velocity, dimensions and test barrel twist are from the SAAMI 8.6 BLACKOUT new cartridge and chamber standard (issued January 19, 2026, revised April 7, 2026). See SAAMI cartridge and chamber drawings.
Is 8.6 Blackout a SAAMI Cartridge?
Yes. SAAMI issued the 8.6 BLACKOUT cartridge and chamber standard on January 19, 2026, and revised it on April 7, 2026. The standard sets a 62,000 psi maximum average pressure, a 200 gr reference load at 2,200 fps, and a 16-inch velocity and pressure test barrel with a 1:6 twist. A published standard means chambers and factory ammunition from different makers are made to the same dimensions.
What Is 8.6 Blackout Used For?
- Suppressed subsonic shooting. Heavy .338 bullets below the speed of sound remove the supersonic crack, so a suppressor only has to deal with muzzle blast. This is the main reason the cartridge exists.
- Hunting. Expanding subsonic bullets for hogs and deer at close range, and supersonic loads for longer shots. See 8.6 Blackout hunting.
- Short barrels. In Chattahoochee Munitions testing, powder use with subsonic loads is effectively complete at 12 to 12.5 inches, so short firearms give up little. See 8.6 Blackout barrel length.
Why Does 8.6 Blackout Use Such a Fast Twist?
A long, heavy bullet moving at only 1,000 fps needs fast spin to stay point-forward. Chattahoochee Munitions offers 1:3 and 1:5 on every 8.6 Blackout firearm. With barrels of about 12.5 inches or longer, its testing has generally favored 1:5 for bullets of about 300 gr and under, and 1:3 for heavy subsonic bullets of about 323 gr and up. SAAMI’s test barrel uses 1:6. The full explanation is in 8.6 Blackout twist rate.
What Firearms Are Chambered in 8.6 Blackout?
8.6 Blackout needs an AR10 or a short-action bolt action. It is too long for an AR15. Chattahoochee Munitions manufactures:
- CM7S bolt action: 8, 12.5 and 16-inch chassis firearms, and 12.5 and 16-inch firearms with walnut WOOX furniture, plus barreled actions. For example, the CM7S 8.6 Blackout bolt action rifle and the CM7S 8.6 Blackout pistol.
- CM10 AR10: 8, 12.5 and 16-inch semi-automatic firearms with customized feed ramps, a Superlative Arms adjustable gas block and an ODIN Works adjustable buffer, such as the CM10 8.6 Blackout AR10 rifle and the CM10 8.6 Blackout SBR.
Every barrel is made by Mos-Tek from 416R stainless steel with E100 Blackout Cerakote. See 8.6 Blackout bolt action vs semi auto for the platform choice.
Who Makes 8.6 Blackout Ammunition?
Factory 8.6 Blackout ammunition is made in smaller runs than common cartridges. Just Cause USA lists 350 and 352 gr Maker REX subsonic loads and a 180 gr supersonic load. Black Butterfly Ammunition lists 305 gr and 352 gr subsonic loads in separate versions for bolt actions and AR10s. See 8.6 Blackout ammo.
How Does 8.6 Blackout Compare?
- 8.6 Blackout vs 300 Blackout: the AR15 subsonic cartridge against the heavier AR10 one.
- 8.6 Blackout vs 308: same bolt face and magazines, different job.
- 8.6 Blackout vs 458 SOCOM: two heavy subsonic big bores.
- 375 Raptor vs 8.6 Blackout and 338 ARC vs 8.6 Blackout.
Explore every 8.6 Blackout firearm, barreled action and magazine in Area 8.6.
What Is 8.6 Blackout FAQ
What is 8.6 Blackout?
8.6 Blackout is a .338-caliber cartridge made from the 6.5 Creedmoor case, designed for heavy subsonic bullets from short, suppressed firearms. SAAMI standardized it in 2026.
What does the 8.6 in 8.6 Blackout mean?
It is the bullet diameter in millimeters: 8.6 mm, which is .338 inch.
Can 8.6 Blackout run in an AR15?
No. It needs an AR10 such as the CM10 or a short bolt action such as the CM7S.
Does 8.6 Blackout use .308 magazines?
It uses .308-length magazines and a .308 bolt face. Chattahoochee Munitions vets the magazines it supplies, including the CM7S 10-round magazine and the CM10 10-round magazine.
What twist rate does 8.6 Blackout use?
Chattahoochee Munitions offers 1:3 and 1:5. SAAMI’s test barrel is 1:6.
Is 8.6 Blackout good for suppressed shooting?
Yes, that is its main purpose. Subsonic bullets remove the supersonic crack. A suppressed firearm still needs hearing protection; see the NIOSH noise guidance.
What is 8.6 Blackout used for?
Mainly suppressed subsonic shooting and hunting hogs and deer from short barrels, with supersonic loads for longer shots.
What is 8.6 Blackout ammo like?
Subsonic loads use 300 to 352 gr bullets at about 1,000 fps; supersonic loads use bullets around 180 to 200 gr. See 8.6 Blackout ammo.
Who makes 8.6 Blackout rifles?
Chattahoochee Munitions manufactures complete 8.6 Blackout firearms: the CM7S bolt action at 8, 12.5 and 16 inches and the CM10 AR10 at 8, 12.5 and 16 inches, each with a 1:3 or 1:5 twist Mos-Tek barrel.