Flash suppressor

A flash suppressor, also known as a flash hider, flash eliminator, or flash cone, is a device attached to a rifle or other gun to reduce the brilliant muzzle flash which occurs upon firing. Muzzle flash is especially visible at night, making it easy to see the location of the shooter, and at the same time destroying the shooter's night vision. It is caused by incandescence of the expanding gases produced by burning gunpowder.

Earlier rifle designs from the 19th century tended to have long barrels that gave the bullets accuracy at what would today be considered very long ranges, perhaps 1,000 yards. A side effect of the long barrel is that the gunpowder is completely burnt before the bullet leaves the barrel. However if the same weapon is "cut down", as is common in cavalry and jungle-combat versions, the bullet would often leave the barrel before the powder was completely burnt. In this case the unburnt powder would ignite in the air, giving off a bright flash.

When barrel lengths dramatically decreased with the introduction of various assault rifles, this flash became a serious problem. Originally limited to "special purpose" roles, it was now expected that all infantry weapons would have short barrels with this problem, and thereby be of limited use in night combat. Flash suppressors became common on post-World War II assault rifle designs, and are almost universal on these weapons today.

It is commonly thought that they are used on military rifles to reduce visibility to the enemy, but the size of a device necessary to hide the muzzle flash from an enemy during the night would be prohibitive. Military flash suppressors are designed to hide the muzzle flash from the shooter to preserve his or her night vision, usually by directing the incandescent gasses downward, away from the line of sight of the shooter. Military forces engaging in night combat are still quite visible, and must move quickly after firing to avoid return fire.

Limiting the amount of powder to what the barrel can burn is one possible solution, but differences between individual cartridges mean that some will always have too much, and the reduced powder load produces a lower projectile velocity. Muzzle flash can also be controlled by using cartridges with a faster-burning gunpowder, so that the propellant gases will already have begun to cool by the time they exit the barrel. Faster-burning powder, however, produces less projectile velocity, which reduces both the accuracy and lethality of the weapon.

Flash suppressors reduce, or in some cases eliminate, the flash by rapidly expanding and cooling the gasses as they leave the end of the barrel. Although the overall amount of burning gunpowder is unchanged, the density and temperature are greatly reduced, as is the brightness of the flash.

A number of different flash hider designs have been used. The simplest is a cone on the end of the barrel, which was used on the jungle-combat versions of the Lee-Enfield. More modern solutions tend to use a "basket" with several slits or holes cut in it, as seen on the M-16 and other small-bore weapons. Flash hiders are often used as a muzzle brake as well, by cutting slits only in the top of the hider, thereby providing some down-force on firing as the gasses escape upwards.

Cone-shaped flash eliminators are evident on the Bren LMG and on the turret-mounted aircraft machine guns of British WWII heavy bombers, which were used mostly at night.