The 8.6 Blackout barrel length that suits subsonic shooting is about 12 to 12.5 inches. In Chattahoochee Munitions testing, powder use with subsonic loads is effectively complete in that range, so a longer barrel adds little speed but a lot of length once a suppressor is fitted. A 16-inch barrel avoids NFA short-barreled rifle paperwork and suits supersonic ammunition. An 8-inch barrel gives a shorter firearm still. Chattahoochee Munitions manufactures 8.6 Blackout firearms at 8, 12.5 and 16 inches.
8.6 Blackout Barrel Length at a Glance
| Barrel | 350 gr subsonic velocity (Just Cause USA) | Fits | Chattahoochee Munitions firearms |
|---|---|---|---|
| 8 inch | 950 fps | Short suppressed package | CM7S and CM10, pistol or SBR |
| 12 to 12.5 inch | 980 fps (12 inch) | Dedicated subsonic, suppressed | CM7S 12.5 inch (CM7 chassis or walnut WOOX furniture), CM10 12.5 inch |
| 16 inch | 1,040 fps | Subsonic and supersonic, no SBR paperwork | CM7S chassis or walnut WOOX furniture, CM10 |
Velocities are published by Just Cause USA for its 350 gr Maker REX subsonic load. Your results will vary with firearm, temperature and ammunition lot.
Why 12 to 12.5 Inches Is the Subsonic 8.6 Blackout Barrel Length
A subsonic load uses a small powder charge, and that charge finishes burning early in the barrel. In Chattahoochee Munitions testing, powder use with subsonic loads is effectively complete at about 12 to 12.5 inches. Past that point, extra 8.6 Blackout barrel length adds little velocity, and a subsonic load cannot go much faster anyway without breaking the sound barrier, about 1,116 fps at 59°F. What the extra length does add is overall length, and a suppressor adds more on top. That is why the 12.5-inch CM7S, in the CM7 chassis or with walnut WOOX furniture, and the 12.5-inch CM10 are the core subsonic configurations.
When Does a 16-Inch Barrel Make Sense?
- No NFA paperwork. A rifle with a barrel of 16 inches or longer is not a short-barreled rifle under federal law.
- Supersonic ammunition. Lighter, faster loads keep gaining velocity past 12 inches. SAAMI’s 200 gr reference load is rated at 2,200 fps from a 16-inch test barrel.
- Mixed use. One firearm for subsonic suppressed shooting and supersonic hunting.
Examples: the CM7S 8.6 Blackout bolt action rifle, the CM7S 8.6 Blackout hunting rifle with walnut WOOX furniture, and the CM10 8.6 Blackout semi auto rifle.
What About an 8-Inch 8.6 Blackout Barrel?
The 8-inch firearms give a short suppressed package. Just Cause USA lists its 350 gr load at 950 fps from 8 inches, only 30 fps below its 12-inch figure. The 8-inch CM7S and CM10 are offered as a pistol with a brace or tailhook, or as an SBR with a stock (an NFA item that requires an approved Form 4). Examples: the CM7S 8.6 Blackout bolt action and the CM10 8.6 Blackout AR pistol.
Does 8.6 Blackout Barrel Length Change the Twist Choice?
Chattahoochee Munitions’ twist guidance is stated for barrels of about 12.5 inches or longer: 1:3 generally favored for subsonic bullets of about 323 gr and up, 1:5 for about 300 gr and under. A shorter barrel gives lower velocity and so less spin from the same twist. See 8.6 Blackout twist rate.
8.6 Blackout Barrel Length and Suppressors
Every inch of barrel adds to the length of a suppressed firearm. A 12.5-inch barrel with a 7 to 8-inch suppressor is about the same length as a bare 20-inch barrel. With subsonic ammunition, an enclosed suppressor is recommended on both the bolt action and the semi-automatic. See 8.6 Blackout suppressor.
Who Makes the Barrels?
Every Chattahoochee Munitions 8.6 Blackout barrel is made by Mos-Tek from 416R stainless steel with 5R rifling and E100 Blackout Cerakote, with a 1:3 or 1:5 twist. The CM7S is also offered as a barreled action, such as the CM7S 8.6 Blackout 12.5-inch barreled action, and the CM10 16-inch barrel is sold as the 8.6 Blackout AR10 barrel.
See every length in Area 8.6, and read 8.6 Blackout ballistics and 8.6 Blackout subsonic.
8.6 Blackout Barrel Length FAQ
What is the ideal 8.6 Blackout barrel length for subsonic?
About 12 to 12.5 inches. In Chattahoochee Munitions testing, powder use with subsonic loads is effectively complete in that range.
Is a 16-inch 8.6 Blackout barrel worth it?
Yes if you want to avoid NFA paperwork or shoot supersonic ammunition. For subsonic use it adds about 60 fps over 12 inches in Just Cause USA’s published figures.
Does an 8-inch 8.6 Blackout barrel lose much velocity?
With subsonic loads, little. Just Cause USA lists 950 fps from 8 inches and 980 fps from 12 inches for its 350 gr load.
Is a short 8.6 Blackout an NFA item?
A rifle with a stock and a barrel under 16 inches is a short-barreled rifle and requires an approved Form 4. The CM7S and CM10 short firearms are also offered in pistol configurations.
What barrel lengths does Chattahoochee Munitions offer in 8.6 Blackout?
CM7S: 8, 12.5 and 16 inches in the CM7 chassis, and 12.5 and 16 inches with walnut WOOX furniture. CM10: 8, 12.5 and 16 inches.
Who makes 8.6 Blackout barrels?
Mos-Tek makes the 416R stainless barrels on every Chattahoochee Munitions 8.6 Blackout firearm, finished in E100 Blackout Cerakote.
Who makes short-barreled 8.6 Blackout rifles?
Chattahoochee Munitions manufactures 8 and 12.5-inch 8.6 Blackout firearms on the CM7S bolt action and the CM10 AR10, offered as pistols or SBRs.