AR-15 Parts: Flash Suppressor
This small piece of the AR-15 is probably one of the most misunderstood parts of the firearm. It gets called a host of different names and is presumed to do a list of diverse chores. Ultimately, the flash suppressor was designed to divert muzzle flash out of the shooters line of sight.
Muzzle flash is caused by excess powder that is still burning when it exits the barrel, hence the flash. If the shooter were in a low light situation without a flash suppressor they would be temporarily unable to see an intended target due to the bright flash at the muzzle. This would prevent the shooter from being able to send a follow up shot.
The shorter the barrel the less time the powder has to burn. This is why most carbine, and medium length barrels usually have a flash suppressor. Some rifle length barrels do not have, nor do they need to have a flash suppressor. What barrel length you choose and type of shooting you do, will predominately determine your need of a flash suppressor.