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FOSSA-556 Flash Hider / Muzzle Device by White Sound Defense

4 reviews

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We have a 90-day no-hassle return policy. We pay return shipping.

If you need to request a return, contact us at and we will send you a return label

After 90 days, defective items will still be covered under the manufacturer’s warranty, where applicable.

Please refer to the product listing for warranty details. If you have specific warranty questions, contact us at We may direct you to pursue your warranty claim directly with the manufacturer.

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If you're dissatisfied with your purchase, in any way, please contact us at - we will do our best to make it right.

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One of the most effective flash hiders on the market, available in Black Oxide or Titanium Nitride finish - the FOSSA-556™ for .223 / 5.56 barrels with a 0.5" x 28 tpi thread

  • Most Effective Flash Reduction
  • Mitigated Dust Signature
  • Compensated Muzzle Rise
  • Reduced Rearward Recoil
  • No Increase in Concussion or Noise
  • No Annoying Ringing Sound

The FOSSA-556™ is a high performance multifunction muzzle device optimized for the fighting rifle. It suppresses muzzle flash and vents gasses away from the ground to limit dust disturbance. It also eliminates muzzle rise and reduces recoil getting the shooter back on target faster, all without increasing concussion or noise.

It is imperative that a muzzle device on a fighting rifle reduce flash to the lowest possible level. Muzzle flash that is visible to the enemy will draw fire. The brighter the flash the greater the distance it will draw fire from. A compromise on muzzle flash brightness is a compromise on position disclosure. Unlike other multifunction devices, the FOSSA-556™ equals or exceeds the flash suppression effectiveness of the very best single function flash suppressors.

The second priority is to improve the effectiveness of fire. Muzzle climb is countered by redirecting propellant gasses with an upward bias. Recoil is reduced by the exclusive tapered (narrowing) vents which force a large percentage of propellant gas to the sides much like a traditional recoil compensator. However, unlike traditional recoil compensators there is no additional concussion or volume.

The FOSSA-556™ has been designed with great care regarding accuracy. It has been engineered and tested to ensure the highest level of performance

Additionally, this device has been tuned to avoid the annoying ringing sound common with other flash suppressors.

This version of the FOSSA-556™ is made from 17-4PH stainless steel and is available with either titanium aluminum nitride or black oxide surface coating. The titanium aluminum nitride finish provides a low friction surface to minimize adhesion of carbon and copper and withstands gas erosion extremely well. The black oxide is a tried and true MIL-DTL-13924 military grade finish.

All muzzle devices represent design compromises. The best design for a competition rifle is not the best design for a fighting rifle. This design is optimized for a fighting rifle. There is no other device that does so much so well.

The current series (002) of this device maintains compatibility with GEMTECH HALO silencers currently deployed.

Note: Some states restrict the use of flash suppressors. It is the responsibility of the purchaser to understand and comply with state and local laws.

This device is patent pending


Q: How should the FOSSA-556™ be oriented (‘clocked’) in relation to the barrel?

A: The widest prong should be at 6 O’clock position. This means that the vent between the two narrow prongs will be straight up at the 12 O’clock position.


Q: How does the FOSSA-556™ mitigate recoil without a traditional baffle?

A: There are several features that contribute to recoil mitigation. The vents on the device decrease in width by about 25% over their length. This narrowing acts as a choke forcing the propellant gases to vent to the sides rather than continuing forward. The central bore geometry and angle of the vent walls are also structured to assist in pushing gases to the side. The recoil reduction is approximately half of what you get from a competition style brake, but without the noise or concussion. Remaining muzzle rise is corrected by the asymmetric vents. The result of these two features is a significant and measureable reduction in split and transition times. 


Q: How will the FOSSA-556™ affect accuracy?

A: This is one of those tricky areas that the marketing folks love to play games with. It is important to understand that muzzle devices can affect accuracy in several ways:

First, they have the potential to create propellant gas flows that disrupt the projectile. Propellant gas flows are very complex systems and it is not always obvious what will and will not affect accuracy. The FOSSA-556™ has been carefully designed and tested to ensure that it does not generate disruptive flows that negatively affect accuracy. It may be of note that most open prong designs do not have gas flow accuracy issues.

The next way a muzzle device can influence accuracy is by changing barrel harmonics by changing the mass near the muzzle. Muzzle devices vary in weight and overall profile. As such, changing muzzle devices will nearly always change point of impact and have some effect on accuracy. A good example of this effect is the Browning BOSS system. It allows the tuning of mass placement to match particular cartridge loads. The same sort of tuning happens when you change muzzle devices. The effect will vary from gun to gun and from specific load to specific load. This is partly why some companies claim their muzzle device can improve accuracy. In some cases, you may improve a specific barrel and load combination by switching to a heavier or lighter muzzle device. In general, the affect is fairly moderate when compared to things like ammo quality and barrel wear.

The last area to talk about is the torque used to attach the muzzle device to the barrel. Excessive torque or a loose muzzle device can have a negative effect on accuracy. For a 5.56/.223 barrel the correct torque is generally between 10 -30 ft/lbs. Those more concerned with accuracy are best served toward the lower side. Those worried about muzzle device separation when removing a suppressor may be better served toward the higher side. A high temperature thread locker will provide additional assurance.


Q: Will permanently attaching the FOSSA-556™ bring my 14.5” barrel up to 16” length?

A: Maybe. The FOSSA-556™ has a fairly deep threaded socket; on some barrels it will only add 1.48” to the length of the barrel. Also, many 14.5” barrels are not exactly 14.5”, so it is important your gunsmith measures carefully and adds shims if needed.

Q: What thread locker is recommended?

A: If no suppressor will be mounted then a high temp medium strength thread locker such as Loctite 246 or other product rated for service at 450F or above works well. If a suppressor is to be mounted, the muzzle device will be subjected to higher temperatures and a specialty thread locker such as Rocksett or Resbond 907TS is appropriate. In all instances, clean and degrease the threads before installation.


Q: Is it better to use crush washers or shims/peel washers for orienting a muzzle device?

A: Crush washers are easier to install, but they should not be used when the muzzle device will function as a suppressor mount. In those cases use a shim or peel washer as required.


Q: Is the FOSSA-556™ intended for use with a sound suppressor?

A: Current production models (002) are compatible with GEMTECH HALO mounting system. In the future, other versions may be made available to fit specific suppressors.


Q: Why do some brands of ammo create ‘sparks’ even when there is no muzzle flash?

A: The type of the power used in some ammo can result in unburned power and glowing bits of debris being blown out the muzzle. This is more common in shorter barreled weapons. All brands of ammo will have occasional ‘sparks’ from a particular round, but some brands (generally the cheaper ones) will throw large numbers of sparks with every round. If you run into this, the solution is to use a brand of ammo that burns more completely and cleanly within the length of barrel you are using. No muzzle device can conceal glowing sparks that actually exit the barrel.

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