How to Pick the Right Muzzle Brake Size for Your Rifle
The most critical factor when choosing a muzzle brake, compensator, or flash device is your bullet’s actual diameter.
Cartridge names can be misleading, so your muzzle brake bore diameter must always match or exceed the bullet diameter for safe, effective performance.
Why Bullet Diameter Matters
Muzzle brakes reduce recoil by venting expanding gases, but their internal bore is sized around the bullet diameter.
If the bore is too small, the bullet can strike the device, a dangerous condition. If it’s too large, the device remains safe but may be slightly less efficient.
Common bullet diameters:
- .223 Remington / 5.56 NATO: ~.224″
- 6.5 Creedmoor: ~.264″
- .300 Win Mag, .308 Win, .30-06 Springfield: ~.308″
Despite different cartridge names, those .30-caliber examples all fire .308″ bullets—so they fit brakes labeled
.30 CAL / .308 / 7.62.
Example: Why a .30 CAL Brake Fits a .300 Win Mag
Do you need a special muzzle brake for .300 Winchester Magnum? In most cases, no. A brake labeled
“.30 CAL” or “.308 / 7.62” is correct because:
- .300 Win Mag uses a .308″ bullet. The name says “.300,” but the bullet’s actual diameter is .308″.
- .308 Win and .30-06 Springfield also fire .308″ bullets.
- Muzzle devices are sized by bullet diameter, not just cartridge names.
Key takeaway: If your cartridge fires a .308″ bullet, choose a device specified for .308 / 7.62 / .30 CAL.
How to Confirm the Correct Fit
- Check bullet diameter: Look up your cartridge’s spec (e.g., .300 Win Mag = .308″).
- Match the device caliber: Select a brake labeled for that diameter (e.g., .308 / 7.62 / .30 CAL).
- Verify thread pitch: Ensure the device matches your barrel threads (common: 1/2-28 for 5.56; 5/8-24 for .30 cal; M18×1 for many European magnums).
- Confirm bore clearance: The brake’s bore must be larger than the bullet diameter to prevent contact.
Quick Reference: Cartridge → Brake Guide
Use this chart as a starting point, then verify thread pitch and manufacturer specs before buying.
| Cartridge | Bullet Diameter | Correct Brake Caliber |
|---|---|---|
| .223 Rem / 5.56 NATO | .224″ | .223 / 5.56 |
| 6.5 Creedmoor | .264″ | 6.5mm / .264 |
| 7mm Rem Mag | .284″ | 7mm / .284 / .30 CAL |
| .308 Win / 7.62 NATO | .308″ | .30 CAL / .308 / 7.62 |
| .300 Win Mag | .308″ | .30 CAL / .308 / 7.62 |
| .30-06 Springfield | .308″ | .30 CAL / .308 / 7.62 |
| .338 Lapua Mag | .338″ | .338 |
| 9mm Luger | .355″ | 9mm |
| .45 ACP | .451″ | .45 |
Other Important Considerations
- Thread Pitch: AR-15 (5.56) barrels are usually 1/2-28; most .30 cal rifles are 5/8-24; many European magnums are M18×1.
- Bore Clearance: The device bore must exceed bullet diameter. Never install a device with a smaller bore.
- Install Per Manufacturer: Follow torque specs and timing procedures (shims, crush washers, or self-timing collars).
- Use Case: Precision shooters may prefer self-timing designs for easy removal; hunters often balance weight and length with recoil reduction.
Ready to upgrade? Explore our muzzle brakes.
FAQs
Can I use a larger-bore brake than my bullet?
Yes. A slightly larger bore is safe and guarantees clearance. You may lose a small amount of recoil reduction efficiency, but it prevents potential bullet contact with the device.
What happens if the device bore is too small?
This is dangerous. A bullet striking the device can cause catastrophic failure, damaging your firearm and risking severe injury or death. Always verify bore size and alignment before use.
Do I match by cartridge name or bullet diameter?
Always match by bullet diameter. For example, .300 Win Mag, .308 Win, and .30-06 all use .308″ bullets and fit devices labeled .308 / 7.62 / .30 CAL.
What else should I check besides caliber?
Confirm thread pitch, shoulder style (square vs. tapered), overall device length/weight, and follow the manufacturer’s installation guidance.