The 8.6 Blackout twist rate is fast: 1:3 to 1:6, compared with 1:10 or 1:12 for a typical .308. Chattahoochee Munitions offers 1:3 and 1:5 on every 8.6 Blackout firearm it manufactures. 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.
8.6 Blackout Twist Rate at a Glance
| Bullet | Typical speed | Twist Chattahoochee Munitions generally favors |
|---|---|---|
| Heavy subsonic, about 323 gr and up (for example 350 and 352 gr) | About 950 to 1,050 fps | 1:3 |
| Subsonic about 300 gr and under (for example 300 and 305 gr) | About 1,000 fps | 1:5 |
| Supersonic, about 180 to 200 gr | About 2,200 fps (SAAMI reference, 200 gr) | 1:5 |
| SAAMI velocity and pressure test barrel | 16 inch | 1:6 |
The bullet guidance applies to barrels of about 12.5 inches or longer and is a practical selection guide from Chattahoochee Munitions testing, not a universal rule. Bullet length and construction matter as much as weight.
Why Is the 8.6 Blackout Twist Rate So Fast?
Stability comes from spin, and spin depends on both twist and velocity. A heavy .338 bullet is long for its weight, and a long bullet needs more spin to stay point-forward. A subsonic bullet moves at roughly half the speed of a typical .308 load, so the barrel has to make up the difference with a faster twist. The 8.6 Blackout twist rate exists to stabilize long subsonic bullets at about 1,000 fps.
Spin in revolutions per minute is muzzle velocity in fps multiplied by 720, divided by the twist in inches:
| Twist | Spin at 1,000 fps (subsonic) | Spin at 2,200 fps (supersonic) |
|---|---|---|
| 1:3 | 240,000 rpm | 528,000 rpm |
| 1:5 | 144,000 rpm | 316,800 rpm |
| 1:6 (SAAMI test barrel) | 120,000 rpm | 264,000 rpm |
| 1:10 (common .308) | 72,000 rpm | 158,400 rpm |
1:3 or 1:5 Twist for 8.6 Blackout?
Choose the 8.6 Blackout twist rate by the bullet you will shoot most.
- 1:3 for heavy subsonic bullets of about 323 gr and up, such as the 350 and 352 gr Maker REX loads from Just Cause USA and the 352 gr Maker Buzz Saw load from Black Butterfly Ammunition.
- 1:5 for bullets of about 300 gr and under, supersonic ammunition, or a mix of loads.
Faster is not automatically better. A 1:3 twist spins a supersonic bullet very fast, and Chattahoochee Munitions generally favors 1:5 when lighter and supersonic bullets are the plan. Ammunition makers also state their own twist guidance; Black Butterfly lists its 305 and 352 gr subsonic loads as tested in a 12.5-inch, 1:3 Chattahoochee Munitions firearm. Follow the ammunition maker’s recommendation for each load.
Why Is the SAAMI Test Barrel 1:6?
SAAMI’s 8.6 BLACKOUT standard (issued January 19, 2026, revised April 7, 2026) specifies a 16-inch velocity and pressure test barrel with a 1:6 twist, and its reference load is a 200 gr bullet at 2,200 fps. The test barrel measures pressure and velocity for the reference load. It is not a recommendation for heavy subsonic bullets, which is why firearm makers offer 1:3 and 1:5. See SAAMI cartridge and chamber drawings.
Does Barrel Length Change the 8.6 Blackout Twist Rate?
Yes. Chattahoochee Munitions’ bullet guidance is stated for barrels of about 12.5 inches or longer. Shorter barrels give lower velocity, and lower velocity means less spin from the same twist. On 8-inch firearms, choose with the ammunition maker’s guidance and confirm on target. See 8.6 Blackout barrel length.
Which Firearms Offer Both 8.6 Blackout Twist Rates?
All of them. Every CM7S bolt action, CM10 AR10 and CM7S barreled action in 8.6 Blackout is offered with a 1:3 or 1:5 twist. Barrels are made by Mos-Tek from 416R stainless steel with 5R rifling and E100 Blackout Cerakote. Examples include the CM7S 8.6 Blackout bolt action rifle, the CM10 8.6 Blackout semi auto rifle and the CM7S 8.6 Blackout barreled action. The twist is chosen on the product page.
More detail on CM’s testing is in 8.6 Blackout subsonic, and every firearm is in Area 8.6.
8.6 Blackout Twist Rate FAQ
What is the 8.6 Blackout twist rate?
Firearms use 1:3 to 1:6. Chattahoochee Munitions offers 1:3 and 1:5, and SAAMI’s test barrel is 1:6.
Is 1:3 or 1:5 better for 8.6 Blackout?
Neither is better for every load. With barrels of about 12.5 inches or longer, Chattahoochee Munitions testing has generally favored 1:3 for subsonic bullets of about 323 gr and up and 1:5 for bullets of about 300 gr and under.
What twist for 8.6 Blackout supersonic ammunition?
Chattahoochee Munitions generally favors 1:5 for lighter and supersonic bullets.
Can a 1:3 barrel shoot 300 gr bullets?
It can, and ammunition makers test some 300-class loads in 1:3. Chattahoochee Munitions testing has generally favored 1:5 for that weight class in barrels of about 12.5 inches or longer.
Why not use a .308 twist for 8.6 Blackout?
A 1:10 twist at subsonic speed gives less than a third of the spin of a 1:3 twist, too little for long, heavy subsonic .338 bullets.
Can I change twist later?
Only by changing the barrel. Pick the twist for the ammunition you plan to shoot most.
Who makes 8.6 Blackout rifles with a choice of twist?
Chattahoochee Munitions manufactures CM7S bolt action and CM10 AR10 firearms in 8.6 Blackout, each with a 1:3 or 1:5 twist Mos-Tek barrel.