8.6 Blackout vs 300 Blackout is a question of how much subsonic bullet you want and which platform you want to carry it. The 300 Blackout fires .308-inch bullets from an AR15 and carries roughly 450 to 490 ft-lb subsonic. The 8.6 Blackout fires .338-inch bullets of 300 to 352 gr from an AR10 or short bolt action and carries roughly 680 to 840 ft-lb subsonic, about half again as much. Chattahoochee Munitions manufactures firearms in both cartridges.
8.6 Blackout vs 300 Blackout at a Glance
| Feature | 8.6 Blackout | 300 Blackout |
|---|---|---|
| Bullet diameter | .338 inch | .308 inch |
| Parent case | 6.5 Creedmoor (.308 Winchester family) | 5.56 / .223 Remington |
| Platform | AR10 or short-action bolt action | AR15 or bolt action |
| Typical subsonic bullet | 300 to 352 gr | 200 to 220 gr |
| Subsonic energy | About 680 to 840 ft-lb | About 450 to 490 ft-lb |
| Supersonic reference | 200 gr at 2,200 fps (SAAMI) | 110 to 125 gr at about 2,200 to 2,350 fps |
| SAAMI maximum average pressure | 62,000 psi | 55,000 psi |
| Typical twist | 1:3 or 1:5 | 1:7 or 1:8 common; 1:5 on the CM7S |
| Ammunition availability | Specialty makers | Widely available |
| Chattahoochee Munitions firearms | CM7S bolt action, CM10 AR10 | CM15 AR15, CM7S bolt action |
8.6 Blackout figures are from SAAMI’s 8.6 BLACKOUT standard and published loads from Just Cause USA and Black Butterfly Ammunition. Pressures are from SAAMI cartridge and chamber drawings.
8.6 Blackout vs 300 Blackout: Which Hits Harder Subsonic?
The 8.6 Blackout. Both cartridges run subsonic loads near 1,000 fps, so energy follows bullet weight. A 350 gr 8.6 Blackout bullet at 980 fps carries about 745 ft-lb. A 220 gr 300 Blackout bullet at 1,000 fps carries about 490 ft-lb. The 8.6 Blackout’s wider .338 bullet also leaves more frontal area to expand. In 8.6 Blackout vs 300 Blackout subsonic terms, the 8.6 Blackout is the step up for hogs and deer.
The Platform Difference: AR15 or AR10
The 300 Blackout fits an AR15: standard lower, standard 5.56 bolt, standard magazines. Only the barrel changes. The 8.6 Blackout is a .308-family cartridge, so it needs an AR10 or a short-action bolt gun with a .308 bolt face. That means more weight and a larger firearm. If you want a smaller, lighter suppressed semi-automatic with AR15 parts, the 300 Blackout fits that job. If you want more bullet, the 8.6 Blackout is worth the larger firearm.
8.6 Blackout vs 300 Blackout Supersonic Performance
With supersonic loads, the 8.6 Blackout pushes a 200 gr .338 bullet at 2,200 fps for about 2,150 ft-lb (SAAMI reference). The 300 Blackout pushes 110 to 125 gr bullets at roughly 2,200 to 2,350 fps for roughly 1,300 to 1,350 ft-lb. The 8.6 Blackout carries more energy at similar speed. See 8.6 Blackout ballistics.
Twist and Barrel Length
Both cartridges are made for short barrels. Chattahoochee Munitions offers 1:3 or 1:5 on every 8.6 Blackout firearm and finds 12 to 12.5 inches effective for 8.6 Blackout subsonic loads. See 8.6 Blackout twist rate and 8.6 Blackout barrel length.
8.6 Blackout vs 300 Blackout Suppressors
A 300 Blackout fires through a .30-caliber suppressor; an 8.6 Blackout needs one rated for .338 or larger. 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 and a flow-through suppressor with supersonic ammunition. See 8.6 Blackout suppressor.
8.6 Blackout vs 300 Blackout: Which Should You Choose?
- Choose 300 Blackout for an AR15-size firearm, widely available ammunition and lower cost per round. Explore Sector 300, including the CM15 300 Blackout AR15 SBR and the CM7S 300 Blackout bolt action, and read 300 Blackout subsonic.
- Choose 8.6 Blackout for heavier subsonic bullets and more energy, on an AR10 or short action. Explore Area 8.6, including the CM7S 8.6 Blackout pistol and the CM10 8.6 Blackout SBR.
More comparisons: 338 ARC vs 8.6 Blackout, 375 Raptor vs 8.6 Blackout and What Is 8.6 Blackout?
8.6 Blackout vs 300 Blackout FAQ
Is 8.6 Blackout better than 300 Blackout?
For heavy subsonic energy, yes: about 680 to 840 ft-lb against about 450 to 490 ft-lb. For size, cost and ammunition availability, the 300 Blackout on an AR15 is the easier choice.
Can 8.6 Blackout run in an AR15 like 300 Blackout?
No. 8.6 Blackout needs an AR10 or a short-action bolt gun.
Is 8.6 Blackout quieter than 300 Blackout?
Both are subsonic at about 1,000 fps. Sound depends mostly on the suppressor, barrel length and firearm, not the cartridge.
Can I use my 300 Blackout suppressor on 8.6 Blackout?
Only if it is rated for .338 or larger. A .30-caliber suppressor is too small for a .338 bullet.
Is 8.6 Blackout ammo more expensive than 300 Blackout?
Yes. 8.6 Blackout ammunition comes from specialty makers in smaller runs.
Is 8.6 Blackout better for hog hunting than 300 Blackout?
Subsonic, the 8.6 Blackout’s heavier, wider bullet carries about half again the energy. See 8.6 Blackout hunting.
Who makes 8.6 Blackout and 300 Blackout rifles?
Chattahoochee Munitions manufactures 8.6 Blackout firearms on the CM7S bolt action and CM10 AR10, and 300 Blackout firearms on the CM15 AR15 and CM7S bolt action.