CMMG Banshee MK4
.300 BLK · 8" pistol
CMMG Dissent
.300 BLK · 10.5"
CMMG Banshee MK4
.300 BLK · 12.5"
Savage 110 Magpul Scout
.300 BLK · 5/8x24
What .300 Blackout was built for
The cartridge was designed around two jobs: fire full-power supersonic loads roughly comparable to 7.62x39, and fire heavy subsonic bullets that pair with a suppressor, all from short barrels on an AR-pattern gun. It uses .30-caliber bullets, so a .30-rated can works.
Barrel length: what changes
| Length | Strengths | Trade-offs |
|---|---|---|
| 8" (Banshee) | Most compact; subsonics run well | More blast and gas; lower supersonic velocity |
| 10.5" (Dissent) | Compact with better supersonic performance | Still gassy suppressed |
| 12.5" (Banshee) | Strong supersonic velocity; smoother running | Longer with a can attached |
| 16" bolt (Savage 110 Scout) | Manual action, so no gas port noise; very quiet | Not semi-auto |
Subsonic physics, briefly
The speed of sound is about 1,125 feet per second at sea level in mild temperatures, and it changes with temperature and altitude. Heavy 200–220gr subsonic .300 BLK loads are designed to stay well below it, so barrel length matters little for staying subsonic. Supersonic loads lose meaningful velocity from very short barrels, which affects range and terminal performance.
Gas and back-pressure
Suppressors raise back-pressure in gas-operated guns. That means more gas at your face and more fouling, especially on short barrels. Adjustable gas blocks, low-back-pressure cans, and good charging-handle seals help. Bolt-action hosts avoid the problem entirely.
Ammo
Magtech .300 BLK 200gr subsonic FMJ
Federal AE .300 BLK 220gr subsonic OTM
Winchester Super Suppressed .300 BLK 200gr
US Cartridge .300 BLK 220gr subsonic FMJ
See subsonic ammo by caliber for more.
Frequently asked questions
Why is .300 Blackout good for suppressed use?
It was designed to shoot heavy subsonic bullets and cycle from short barrels, and it works with .30-caliber suppressors.
Does barrel length affect subsonic .300 BLK?
Heavy subsonic loads generally stay below the speed of sound across common barrel lengths. Supersonic loads lose more velocity from short barrels.
Will it cycle subsonic?
Many .300 BLK guns cycle subsonic loads, especially suppressed, but reliability varies by gas system. Test with your load and can.
Pistol or rifle — which needs NFA paperwork?
A .300 BLK pistol is sold as a pistol. Adding a shoulder stock to a short barrel creates a short-barreled rifle, which falls under separate federal rules that are changing in 2026. Check current law.
Keep reading
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