There seems to be quite a lot of confusion about these devices, so I thought I would start a thread on them with some history on their use on U.S. Military Small Arms.
Arguably, the first widely used Flash Supprssors (FS's) on GI Infanty weapons was on the M1918 Browning Automatic Rifle. The idea of a Flash Suppressor was and is that when you have to shoot at night, the FS redirects or "breaks up" some of the burning gas that comes out the muzzle so there is no large fire ball that easily gives your position away to the enemy. ALSO, a large fire ball messes up your night vision more than the muzzle blast redirected by a Flash Suppressor. A large fire ball is easier to see and shoot at than when it gets redirected or broken up. Normally on a FS, there are slots all the way around the FS and you see some kind of "star" shaped fire coming from the muzzle.
OK, a few years later a neat innovation came along as the "Cutts Compensator" and was used on the Thompson Sub Machine Gun. There were slots along the TOP of the compensator, but the bottom was solid. The slots on top still broke up a solid fireball muzzle blast, but the solid bottom helped keep the muzzle from rising in recoil. The way it works is the gas coming out the barrel expands all around the muzzle evenly. Some gas work against the solid bottom of the compesator and that is what helps keep the muzzle from rising as much. The rest of the gas goes up and through slots on top and of course some comes out the muzzle. ANOTHER advantage of a compensator with a solid bottom is that when you are in the prone position in a dusty or sandy environment, the gas of the muzzle blast does not kick dust or sand up in front of you as much as a FS or nothing on the end of the barrel.
When the M1 Garand came along, they decided they wanted to make a Flash Hider for it for Sniper use as the M1 C. They developed the coned shape M2 Flash Hider. However, due to the weight of them on the muzzle, they messed up barrel harmonics and snipers often had the Armorers REMOVE the M2 Flash Hiders for the best accuracy. The four prong T37 Flash Suppressor came along in the195O's. There seems to be some disagreement when they were first used. Some sources say they were used on the M1 D rifles the Marine Corps built in 1952. Other sources say the T37 did not come out until 1955. I don't know which is correct. However, the T37 had alignment issues when mounting them and from rough handling in combat PLUS that is a LOT of weight to hang off the rifle muzzle and messes up the barrel harmonics and thus DECREASES accuracy, it proved not very popular in Sniper use. Snipers usually had the Armorers take them off as well.
When they decided to make a Flash HIDER for M1 Carbine, they copied and basically scaled down the M2 Flash HIDER for the M1 Garand. Bill Ricca has an EXCELLENT information page on these in the link below: http://www.billricca.com/carbfh.htm
So the term "Flash HIDER" is really only correct for the M2 FH for the Garand and the M3 FH for the Carbine. Unfortunately that is what started the confusion between Flash HIDERS and Flash SUPPRESSORS. Bottom line, a Flash HIDER is cone shaped and that is the easiest way to remember the difference.
When they developed the M14, they put a Flash Suppressor on EVERY rifle because ANY M14 could be adapted for select fire. However, this Flash Supressor was not JUST a Flash Suppressor. It ALSO has a solid part on the bottom to help resist muzzle rise and not stir up ground dust or sand as much when the rifle is fired from the prone position. So they could and maybe should have called it a Compensator instead of a FS. However, they called it a Flash Suppressor, so that's what it is.
They sort of back tracked at first for the M16 series of rifles. The first FS was three pronged followed by the closed end "bird cage" FS. Finally in the M16A2, they took a lesson from the M14 and introduced a new model and a new name for US military rifles with the solidTo bottom "Compensator." The Compensator once again kept the rifle from blowing too much dust or sand up in front of the shooter.
To my knowledge, the Barrett .50 Cal. Sniper Rifle introduced the term "Muzzle BRAKE" to the U.S. Military. People get this mixed up with the word "BREAK," but the device doesn't break anything and certainly not the muzzle. Grin. It is correctly spelled "BRAKE" as in "putting the brakes on" in a car. Muzzle Brakes work by directing at least some of the muzzle blast angling back towards the shooter. There are two HUGE angled plates in the Barrett Brake that angles part of the muzzle blast backward and what it does is push the rifle FORWARD a bit in recoil. It is something like two rocket engines, one on each side of the Brake, pushing the rifle forward due to the muzzle blast angling to the rear. Normally a Muzzle Brake redirects some of the muzzle blast to the rear.
I'll close with one last Muzzle Device that has most recently entered the U.S.Miitary with the Model M40A5 Sniper Rifle and that is a "Sound Suppressor." The Marine Corps does not call it a "Silencer" because it does not totally silence the muzzle blast of the rifle and because the word "Silencer" has come to inherently have bad connotations in meaning. The main difference between a Flash Suppressor and a Sound Suppressor is the Sound Suppressor is the Sound Suppressor reduces the noise of the muzzle blast.