Muzzle brakes and recoil compensators are devices that are fitted to the muzzle of a firearm or cannon to redirect propellant gases with the effect of countering both recoil of the gun and unwanted rising of the barrel during rapid fire. Muzzle brakes are very useful for combat and timed competition shooting, and are commonly found on rifles firing very large cartridges (often big-game rifles), as well as some artillery and tank guns. They are also commonly used on pistols for practical pistol competitions, and are usually called compensators in this context.
There are a large number of terms, including muzzle brake, recoil compensator, compensator, recoil brake, recoil check, Mag-na-port, and more, which all refer to devices that serve to direct propellant gases upwards, outwards, or rearwards to reduce muzzle climb and recoil. These range from the simple slotted barrel of the original Mag-na-porting to the Schuemann "hybrid" system, which mates a specially ported barrel and slide with a threaded compensator for maximum reduction of muzzle rise. With the exception of names for proprietary systems, such as Mag-na-porting and hybrid compensators, and brand names such as Muzzle Tamer, the various terms are used interchangeably.
The primary reason for muzzle rise is that for nearly all firearms, the centerline of the barrel is above the center of contact between the shooter and the firearms' grips and stock. The forces from the bullet being fired and the propellant gases exiting the muzzle act directly down the centerline of the barrel. If that line of force is above the center of the contact points, this creates a moment or torque rotational force. That torque causes the firearm to rotate, and the muzzle end to rise upwards.
Firearms with less height from the grip line to the barrel centerline will tend to experience less muzzle rise.
Muzzle brakes are simple in concept. One of the simplest designs can be found on U.S. 90 mm tank guns as used on the M47 Patton tank. This consists of a small length of tubing mounted at right angles to the end of the barrel. Brakes most often utilize slots, vents, holes, baffles, and similar devices. The strategy of a muzzle brake is to redirect and control the burst of combustion gases that follows the departure of a projectile.
In conventional muzzle brake designs, combustion gases depart the muzzle brake at an angle (or direction) to the muzzle. This creates a force which helps to counteract the rearward movement of the barrel (due to recoil) as well as the upward rise of the muzzle. The effect can be compared to reverse thrust systems on aircraft jet engines. The mass and velocity of the gases is significant enough to move the firearm in the opposite direction of recoil. On the AKM assault rifle, the brake is angled slightly to the right to counteract the sideways movement of the gun under recoil.
Another method of redirecting gases is called porting. Porting involves creating ports or holes that are precision-drilled into the forward part of the barrel (and slide on pistols). These holes are designed to divert a portion of the gases expelled prior to the departure of the bullet in the direction that reduces the tendency of the firearm to flip upwards. The concept applies Newton's third law: the exhaust directed upward causes a reciprocal force downward. Porting is most commonly used on shotguns, where recoil is most significant and makes rapid firing difficult. Even single shots of magnum-strength loads are uncomfortable for all but the most-seasoned shooters. Porting has obvious advantages for faster follow-up shots, especially for 3-round burst operation. However, in most instances porting does nothing to enhance the accuracy of follow-up shots.
Another strategy (besides redirecting gases) for counteracting muzzle rise involves slowing the departure of combustion gases. Slowing of the gases is the method used on suppressors and linear compensators.
Construction of a brake or compensator can be very simple; for example, some models of the AK-47 used a diagonal cut at the muzzle end of the barrel to direct some of the escaping gases upwards. Another simple method is porting, where holes or slots are machined in the barrel near the muzzle to allow the gas to escape.
More advanced designs use baffles and expansion chambers to slow down the escaping gases; this is the basic principle behind a linear compensator. Ports are often added to the expansion chambers, producing the long, multi-chambered recoil compensators often seen on IPSC raceguns.
There are advantages and disadvantages to muzzle brakes. Recoil is a subjective concept. One shooter may perceive it as pain, another as movement of the sights, and another as rearward thrust. Recoil energy can be sharp if the impulse is fast or may be considered soft if the impulse is slower, even if the same total energy is transferred.
Though there are numerous ways of measuring the energy of a recoil impulse, it's generally true that between 10% and 50% reductions can be measured. There are however muzzle brake manufacturers that claim greater recoil reduction percentages. Muzzle brakes need sufficient propellant gas volume and high gas pressure at the muzzle of the gun to achieve good measured recoil reduction percentages. This means cartridges with a large bore area to case volume ratio combined with a high operating pressure benefit more from recoil reduction with muzzle brakes than smaller standard cartridges.
Besides reducing felt recoil one of the primary advantages of a muzzle brake is the reduction of muzzle rise. This allows a weapon's sights to be realigned more quickly. This is relevant particularly for fully automatic weapons. Muzzle rise is often entirely eliminated by an efficient design. Because the rifle moves rearward less, the shooter has little to compensate for. This is particularly true of rapid-fire, fully-automatic fire, and large-bore hunting rifles. They are also common on small-bore varmint rifles, where reducing the muzzle rise allows the shooter to see the bullet impact through a telescopic sight. A reduction in recoil also reduces the chance of undesired (painful) contacts between the shooters head and the ocular of a telescopic sight or other aiming components that have to be positioned near the shooters eye. Another advantage of a muzzle brake is a reduction of recoil fatigue during extended practice sessions, enabling the shooter to consecutively fire more rounds accurately. Further, flinch (involuntary pre trigger release anxiety behaviour resulting in inaccurate aiming and shooting) caused by excessive recoil may be significantly reduced or eliminated with certain shooters.
The advantages of brakes and compensators are not without cost, however. The most obvious of these to the shooter or gun crew is the perceived increase in sound pressure level as well as the increase in muzzle blast for the shooter or gun crew. This occurs because the sound, flash, and pressure waves normally projected largely away from the shooter are now partially-redirected outwards to the side or even at backward angles towards the shooter or gun crew. While eye and ear protection should always be used when shooting, even this is not enough to avoid hearing damage with the muzzle blast directed back towards the shooter or gun crew.
"Recorded noise levels (on certified audiological instruments) at the muzzle of a magnum or high velocity rifle with a muzzle break [sic] normally exceed 160 decibels. Permanent ear damage occurs at 120 decibels. If you read the fine print on the finest set of ear plugs and ear muffs available, you will find the total noise reduction only between 22 and 31 decibels. This means that on a rifle with a muzzle brake, even if you are wearing hearing protection, you are suffering permanent damage."
Measurements indicate that on a rifle a muzzle brake adds 5 to 10 dB to the normal noise level perceived by the shooter, increasing total noise levels up to 160 dB(A) +/- 3 dB.. Painful discomfort occurs at approximately 120 to 125 dB(A), with some references claiming 133 dB(A) for the threshold of pain.[18 ] Active ear muffs are available with electronic noise cancellation that can reduce direct path ear canal noise by approximately 17-33 dB, depending on the low, medium, or high frequency at which attenuation is measured. Passive ear plugs vary greatly in their measured attenuation, ranging from approximately 20 dB to 30 dB, depending on whether or not they are properly used. Using both ear muffs (whether passive or active) and ear plugs simultaneously is a practice that is often used for obtaining the maximum protection, but the efficacy of such combined protection relative to preventing permanent ear damage is not conclusive, with evidence indicating that a combined noise reduction ratio (NRR) of only 36 dB (C-weighted) is the maximum possible using ear muffs and ear plugs simultaneously, equating to only a 36 - 7 = 29 dB protection against a 160 dB(A) noise level.[18 ] Relative to a noise level of 160 dB(A), this means that even using ear muffs and ear plugs simultaneously cannot protect a shooter against permanent ear damage when using a muzzle brake, through leaving a shooter exposed to noise levels of approximately 131 dB(A) that is 11 dB above the point where permanent ear damage occurs.
In the European Union (EU), employees are protected by law against impulsive or impact noise exposure over 137 dB(A), with an absolute limit of 140 dB(A). Individual member states often define even lower levels by national law; the United Kingdom, for instance, opted for 120 dB(A), which is where many references indicate that permanent ear damage occurs. The duration of exposure is likewise limited, for environmental noise above 90 dB(A) in the United States by OSHA rules, and for environmental noise above 80 dB(A) in the European Union, for exposure over an entire work day. The EU legislation demands the noise has to be reduced at the origin in the technically best possible way. Professional small arms and artillery users such as military and police personnel, etc., have to be issued with adequately working suppressors or hearing protection to reduce noise to levels as defined by law, since an employer has to anticipate legal action and compensations in cases where an employee that used the provided protective gear suffers work-induced health damage.
Brakes and compensators are additionally often quite bulky, adding length, diameter, and mass to the muzzle end of the firearm, where it will most influence its handling. Further, flinch caused by blast induced sinus cavity concussion discomfort experienced by the shooter can become a problem for anti-materiel rifle shooters due to the big cartridges these rifles fire.
A serious tactical disadvantage of muzzle brakes on both small arms and artillery is that, depending on their designs, they may cause escaping gases to throw up dust and debris clouds that impair visibility and reveal one's position. Troops often wet the ground in front of antitank guns in defensive emplacements to prevent this, and snipers are specially trained in techniques for suppressing or concealing the magnified effects of lateral muzzle blast when firing rifles with such brakes. Linear compensators and suppressors do not have the disadvantages of a redirected muzzle blast; they actually reduce the blast by venting high pressure gas forward at reduced velocity.
Muzzle brakes were ruled "legal" by the ATF in the United States a short time after the now defunct Federal assault weapons ban went into effect in 1994. These muzzle attachments were legal to attach to a threaded barrel, so long as they were welded in place on certain firearms (high temperature silver solder also sufficed). On the other hand, flash suppressors, and barrel shrouds were seen as 'military' features, and were on the list of features that, provided enough features were also present on the semi-automatic rifle, then the rifle was defined as illegal, if manufactured after the effective date of the ban. This meant, in practice, muzzle brakes had to be certified by the ATF to prevent end-users from accidentally violating the law and installing a device that could later be found to be defined legally as being more of a flash suppressor than a muzzle brake, even if marketed and sold as a muzzle brake, if incidental flash suppression was deemed to be 'significant' by the ATF. The Federal laws governing this sunsetted in 2004, and are no longer of active concern, except in those few jurisdictions in which certain provisions are still retained in specific state laws.