Flash suppressor A flash suppressor , also known as a flash guard , flash eliminator , flash hider , or flash cone , is a device attached to the muzzle of a rifle that reduces its visible signature while firing by cooling or dispersing the burning gases that exit the muzzle , a phenomenon typical of carbine length weapons . Its primary intent is to reduce the chances that the shooter will be blinded in low light shooting conditions . Contrary to popular belief , it is only a minor secondary benefit if a flash suppressor reduces the intensity of the flash visible to the enemy . Although they are typically mounted in the same position and sometimes confused with each other , a flash suppressor is different from a muzzle brake . While the former is intended to reduce visible flash , a muzzle brake is designed to reduce painful recoil inherent to large cartridges and typically has no effect on visible flash . Rationale . Pre - 20th century rifle designs tended to have longer barrels than modern rifles . A beneficial side effect of the long barrel is that the propellant is completely burnt before the bullet leaves the barrel , usually resulting only in a puff of smoke from the muzzle . However , if the same weapon ' s barrel is " cut down " ( shortened ) , as is common in cavalry and jungle - combat adapted versions , the bullet would often leave the barrel before the powder was completely consumed , resulting in a bright flash from the muzzle . When barrel lengths were dramatically decreased with the introduction of various shorter barreled rifles and carbines , the flash became a serious problem during night - time combat , as the flash would imperil the shooter ' s night vision . Originally limited to " special purpose " roles , it was now expected that all infantry weapons with shorter barrels would experience this problem , and thereby be of limited use in low light situations . Flash suppressors became common on late - World War II and later assault rifle designs , and are almost universal on these weapons today . Some designs such as those found on the AKS - 74U serve a dual - role as a gas expansion chamber helping the shortened weapon ' s gas system function properly . Military flash suppressors are designed to reduce the muzzle flash from the weapon to preserve the shooter ' s night vision , usually by diverting the incandescent gases to the sides , away from the line of sight of the shooter , and to secondarily reduce the flash visible to the enemy . Military forces engaging in night combat are still visible when firing , especially with night vision gear , and must move quickly after firing to avoid receiving return fire . Limiting the amount of powder to what the length of a barrel can burn is one possible solution , but differences between individual cartridges mean that some cartridges will always have too much powder to be completely consumed , and the reduced powder load produces a lower projectile velocity . Muzzle flash can be controlled by using cartridges with a faster - burning propellant , so that the propellant gases will already have begun to cool by the time they exit the barrel , reducing flash intensities . Faster - burning powders , however , produce less projectile velocity , which reduces the accuracy due to introducing more of a parabolic bullet flight path in place of a " flat " trajectory while also reducing lethality of the weapon by reducing the energy delivered on target . Flash suppressors reduce , or in some cases eliminate , the flash by rapidly cooling the gases as they leave the end of the barrel . Although the overall amount of burning propellant is unchanged , the density and temperature are greatly reduced , as is the brightness of the flash . Types . A number of different flash suppressing designs have been used over the years . The simplest is a cone placed on the end of the barrel , which was used on the late - World War II jungle - combat versions of the Lee - Enfield , the No . 5 variant , intended for use in the Pacific . More modern solutions tend to use a " basket " with several slits or holes cut in it , as seen on the M16 and other small - bore weapons . Cone - shaped flash eliminators are also evident on the Bren LMG and on the turret - mounted aircraft machine guns of British WWII heavy bombers , which were used mostly at night . Duckbill flash suppressors have upper and lower " prongs " and direct gases to the sides . Early M60 machine gun s and some early M16 models featured this type of flash suppressor . One disadvantage is that the prongs can become entangled with vines or other natural vegetation and objects in the field . The Vortex Flash Hider is a design made by Smith Enterprise Inc . and has been called the " most effective flash hider available short of a ( sound ) suppressor " by writer and gunsmith Patrick Sweeney , when used on an AR15 . Smith makes this design for over 25 different rifles and handguns . This design prevents the possible entanglement of vegetation between the flutes . " Birdcage type " flash suppressors still have prongs , but feature a ring on the front to prevent vegetation entanglement between the prongs . The closed bottom port of the M16A2 design makes the device function as a compensator . Both designs require indexing with a crush washer which unfortunately contributes to flash signature . The Noveske KX - 3 is a flash suppressor intended for use on shorter barreled rifles and aids in reliability . The back pressure generated through this type of flash suppressor helps to cycle the rifle . Noveske patterned this design on the Krinkov brake found on the Soviet AK74SU submachinegun , where it was explicitly used for this purpose . Essentially it is the cone - shaped suppressor of the AK74SU within a chamber . Some other examples of cone - shaped hiders are found on the Bren machine gun , the . 303 Rifle No 5 Mk 1 " Jungle Carbine " and some models of the RPK and German MG3 . The XM177 Commando variant of the M16 rifle used a unique flash suppressor sometimes called a flash or sound moderator for its 10 - inch barrel . This device is 4 . 2 inches long and was designed primarily as a counterbalance measure as the shorter barrel made the weapon unwieldy . This device reduced flash signature greatly and sound signature slightly , making the normally louder short barreled rifle sound like a longer barreled M16A1 . Although it has no internal baffles and does not completely reduce the sound signature to subsonic levels , because it alters the sound level of the weapon , the US Bureau of Alcohol Tobacco Firearms and Explosives has declared this device to be a sound suppressor and regulates its civilian purchase in the United States . There are also devices referred to as hybrids that function as both flash suppressors and muzzle rise / recoil compensators such as the White Sound Defense FOSSA - 556 . The U . S . military A2 muzzle device is technically a hybrid device as it has vents that are biased upwardly to reduce muzzle rise . Legality . New Zealand . Flash suppressors are seen as a " military " feature , and semi - automatic long guns with suppressors were defined as Military - Style Semi - Automatic s in 1992 , requiring a permit . United States . Flash suppressors and barrel shroud s were seen as ' military ' features , and were on the list of Federally defined features that could cause a rifle to be defined as illegal , if manufactured after the effective date of the Federal Assault Weapons Ban that went into effect in 1994 in the United States . This ban expired in 2004 , although some states such as California and New York have similar bans in place restricting the use of flash suppressors .