8.6 Blackout vs 308 compares two cartridges from the same family that can both be shot subsonic. Both use the .308 Winchester bolt face, the same 62,000 psi SAAMI pressure limit and .308-length magazines. Chattahoochee Munitions manufactures firearms in both, and it loads its own 308 Winchester subsonic ammunition: a 300 gr Maker REX at an average of 1,005 fps from a 12.5-inch, 1:5 twist barrel. The 8.6 Blackout puts a heavier .338 bullet in a shorter case and runs subsonic or supersonic from the same barrel. The .308 Winchester needs a dedicated 1:5 subsonic firearm for its 300 gr load and a conventional firearm for supersonic shooting.
8.6 Blackout vs 308 at a Glance
| Feature | 8.6 Blackout | 308 Winchester |
|---|---|---|
| Bullet diameter | .338 inch | .308 inch |
| Case | From 6.5 Creedmoor, 1.685 inch | Parent of the family, 2.015 inch |
| Bolt face | .308 | .308 |
| Maximum cartridge length | 2.810 inch | 2.810 inch |
| SAAMI maximum average pressure | 62,000 psi | 62,000 psi |
| Subsonic bullet | 300 to 352 gr | 300 gr Maker REX (Chattahoochee Munitions load) |
| Subsonic velocity and energy | About 980 to 1,000 fps, about 745 to 780 ft-lb (published 350 and 352 gr loads, 12 to 12.5 inch) | 1,005 fps average, 673 ft-lb (12.5 inch, 1:5) |
| Twist for subsonic | 1:3 or 1:5 | 1:5 required |
| Twist for supersonic | The same 1:3 or 1:5 barrel | 1:8 or 1:10 (a separate firearm) |
| Subsonic and supersonic in one semi-automatic | Yes: CM10 with adjustable gas and buffer | No: the CM10 SUBSONIC is for the subsonic load only |
| Subsonic ammunition source | Just Cause USA, Black Butterfly | Chattahoochee Munitions |
Pressures and dimensions are from SAAMI cartridge and chamber drawings. 8.6 Blackout figures are published by Just Cause USA and Black Butterfly; 308 figures are Chattahoochee Munitions data.
What Do 8.6 Blackout and 308 Share?
The 8.6 Blackout comes from the 6.5 Creedmoor case, which itself comes from the .308 Winchester family. The case head, bolt face and maximum cartridge length are the same, and both feed from .308-length magazines. Both run in a Remington 700 footprint short action such as the CM7S and in a large-frame AR10 such as the CM10.
8.6 Blackout vs 308 Subsonic
Both cartridges carry roughly 300 to 350 gr of bullet at about 1,000 fps, so the subsonic comparison is closer than the case sizes suggest.
- 308 Winchester subsonic: Chattahoochee Munitions loads the 300 gr Maker REX, a lead-free solid copper expanding bullet 2.06 inches long, in new Starline brass. From a 12.5-inch, 1:5 barrel it averages 1,005 fps with a standard deviation of 2.44 fps over 10 rounds, for 673 ft-lb at the muzzle and 644 ft-lb at 100 yards. See the 300 gr 308 subsonic ammo.
- 8.6 Blackout subsonic: the larger case and .338 diameter take heavier bullets. Just Cause USA lists its 350 gr Maker REX at 980 fps from 12 inches, about 745 ft-lb, and Black Butterfly lists 352 gr loads at about 1,000 fps from a 12.5-inch 1:3 barrel, about 780 ft-lb.
So the 8.6 Blackout carries roughly 10 to 15 percent more subsonic energy and a wider .338 bullet. The .308 subsonic load has Chattahoochee Munitions’ own velocity data and range card behind it, and 308 Winchester brass is easy to find. Both bullets expand, and both are close-range loads.
Twist Rate: 8.6 Blackout vs 308
The 2.06-inch, 300 gr .308 bullet needs a 1:5 twist at subsonic velocity. Conventional 308 barrels are 1:8 or 1:10, and Chattahoochee Munitions warns never to fire its 300 gr subsonic load through them: an unstable bullet can yaw and strike a suppressor baffle. A 308 subsonic firearm is therefore a dedicated configuration.
The 8.6 Blackout was designed around fast twist from the start. Chattahoochee Munitions offers 1:5 for bullets of about 300 gr and lighter and 1:3 for heavy subsonic bullets of about 323 gr and up, and the same barrel also fires supersonic 8.6 Blackout. Read 8.6 Blackout twist rate.
Semi-Automatic Subsonic: CM10 SUBSONIC vs CM10 8.6 Blackout
Low-pressure subsonic ammunition does not cycle a conventional AR10. Chattahoochee Munitions solves that in two different ways:
- 308: the CM10 308 SUBSONIC is a 12.5-inch, 1:5 AR10 configured for the 300 gr load. It cycles with an enclosed suppressor attached, and it must not fire supersonic ammunition.
- 8.6 Blackout: the CM10 8.6 Blackout uses a Superlative Arms adjustable gas block and an ODIN Works adjustable buffer, so one firearm can be tuned for subsonic ammunition with a suppressor or for supersonic ammunition. See the 8.6 Blackout subsonic AR10.
On a bolt action the difference shrinks. The CM7S is manually operated, so it fires subsonic ammunition with or without a suppressor and needs no tuning. Compare the CM7S 308 12.5-inch 1:5 bolt action with the 12.5-inch 8.6 Blackout bolt action pistol. Read 8.6 Blackout bolt action vs semi auto.
8.6 Blackout vs 308 Supersonic and at Distance
The .308 Winchester. Its longer case pushes 150 to 180 gr bullets well over 2,500 fps from a full-length barrel, with a flatter path and long-range data everywhere. The 8.6 Blackout’s SAAMI reference is a 200 gr bullet at 2,200 fps from 16 inches. Subsonic, neither is a long-range load: with a 100-yard zero, Chattahoochee Munitions’ 300 gr .308 load drops about 34.6 inches at 200 yards and 106.6 inches at 300 yards.
8.6 Blackout vs 308 Barrel Length
For subsonic shooting both work from 12.5 inches. Chattahoochee Munitions tests its 308 subsonic load in 12.5-inch barrels, and in its testing 8.6 Blackout subsonic loads finish burning their powder at about 12 to 12.5 inches. For supersonic use the .308 needs longer barrels to reach its velocity. Chattahoochee Munitions manufactures the 8.6 Blackout at 8, 12.5 and 16 inches. See 8.6 Blackout barrel length.
8.6 Blackout vs 308 Suppressors
A .308 fires through a .30-caliber suppressor; an 8.6 Blackout needs a .338 or larger rating. A .338 suppressor such as the PLACID 375 works on both. On a bolt action use an enclosed suppressor. On a semi-automatic, use an enclosed suppressor with subsonic ammunition (the CM10 308 SUBSONIC needs one to cycle) and a flow-through suppressor with supersonic ammunition (not for use in the CM10 308 SUBSONIC). See the 8.6 Blackout suppressor guide and the 308 suppressor guide.
8.6 Blackout vs 308: Which Should You Choose?
- Choose 308 Winchester subsonic if you want Chattahoochee Munitions’ own 300 gr Maker REX load with published velocity and drop data, in a dedicated 12.5-inch 1:5 firearm. Explore District 308 and read 308 Winchester subsonic.
- Choose 308 Winchester supersonic for shooting at distance with ammunition you can buy anywhere, such as the CM7S 308 bolt action rifle or the CM10 308 AR10 rifle.
- Choose 8.6 Blackout for heavier .338 subsonic bullets and one firearm that shoots subsonic and supersonic. Explore Area 8.6, including the CM7S 8.6 Blackout bolt action rifle and the CM10 8.6 Blackout AR10 rifle.
Read more in What Is 8.6 Blackout?, 8.6 Blackout subsonic and the .308 Winchester cartridge family.
8.6 Blackout vs 308 FAQ
Is 8.6 Blackout based on the 308?
It comes from the 6.5 Creedmoor case, which belongs to the .308 Winchester family. It shares the .308 bolt face and maximum cartridge length.
Can 308 Winchester be shot subsonic?
Yes, with the right bullet and twist. Chattahoochee Munitions loads a 300 gr Maker REX at an average of 1,005 fps from a 12.5-inch barrel, and it requires a 1:5 twist. Do not fire it in a 1:8 or 1:10 barrel.
8.6 Blackout vs 308 subsonic: which hits harder?
The 8.6 Blackout, by about 10 to 15 percent, because it takes 350 to 352 gr bullets at about the same speed. The 300 gr .308 load carries 673 ft-lb at the muzzle.
Will 308 subsonic cycle an AR10?
Not a conventional one. The CM10 308 SUBSONIC cycles Chattahoochee Munitions’ 300 gr load with an enclosed suppressor attached, and it is for that load only.
Can one firearm shoot 8.6 Blackout subsonic and supersonic?
Yes. The same 1:3 or 1:5 barrel fires both, and the CM10 8.6 Blackout’s adjustable gas block and buffer tune it for either. A CM7S bolt action needs no tuning.
Does 8.6 Blackout use 308 magazines?
It uses .308-length magazines. Chattahoochee Munitions vets the magazines it supplies with its 8.6 Blackout firearms.
Can I fire 308 in an 8.6 Blackout?
No. Never fire any cartridge in a chamber not marked for it.
Who makes 8.6 Blackout and 308 subsonic rifles?
Chattahoochee Munitions manufactures both on the CM7S bolt action and the CM10 AR10, including the 12.5-inch 1:5 CM7S 308 and the CM10 308 SUBSONIC, and it loads the 300 gr 308 subsonic ammunition.