Muzzle brakes and recoil compensators are devices that are either fitted to, or designed as a permanent part of, 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 useful for combat and timed competition shooting, and are commonly found on rifles firing large cartridges (such as big-game rifles), as well as some artillery and tank guns. They are also used on pistols for practical pistol competitions, and are usually called compensators in this context.
The term muzzle brake was introduced in the context of artillery, but it is also used for rifles and pistols. It defines a device that reduces the recoil of the weapon by directing the propellant gases sideways and backwards. The force generated at the muzzle brake baffles or ejector ports acts in the opposite direction to the force of recoil, thus reducing wear on the recoil-damping mechanism and allowing a lighter design. In the case of smaller caliber firearms such as rifles it reduces the effects of kickback on the shooter.
The terms recoil brake and recoil check are seldom used and never in artillery parlance. The terms recoil compensator, compensator, Mag-na-port and others belong to shooters' lingo and refer to devices that serve to direct propellant gases upwards to reduce muzzle climb and to some extent also the recoil in hand firearms like pistols and revolvers, and also in small-calibre automatic weapons like assault rifles, PDWs etc. 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 in the hand firearm parlance are used interchangeably.
Muzzle rise or climb 
The muzzle rises primarily because for most 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, causing the firearm to rotate and the muzzle end to rise upwards. The M1946 Sieg automatic rifle had an unusual muzzle brake that made the rifle climb downwards, but enabled the user to fire it with one hand in full automatic.
Firearms with less height from the grip line to the barrel centerline tend to experience less muzzle rise.
Muzzle brakes are simple in concept, such as the 90 mm M3 gun which is 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.
All muzzle brake designs share a basic principle: combustion gases are partly diverted at a generally sideways angle away from the muzzle end of the bore. The resulting change in the gases' momentum creates a reaction 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 the reverse thrust system on an aircraft jet engine.
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 and shotguns). 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.
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 muzzle brake or compensator can be as simple as a diagonal cut at the muzzle end of the barrel to direct some of the escaping gas upwards. On the AKM assault rifle, the brake is additionally angled slightly to the right to counteract the sideways movement of the rifle under recoil.
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 may be perceived by different shooters as pain, movement of the sight line, rearward thrust, or some combination of the three. 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, in general a 10% to 50% reduction can be measured. Some muzzle brake manufacturers 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 for fully automatic weapons. Muzzle rise is often eliminated by an efficient design. Because the rifle moves rearward less, the shooter has little to compensate for. Muzzle brakes benefit rapid-fire, fully automatic fire, and large-bore hunting rifles. They are also common on small-bore vermin 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 shooter's head and the ocular of a telescopic sight or other aiming components that have to be positioned near the shooter's eye (often referred to as "scope 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 reduced or eliminated with certain shooters.
The advantages of brakes and compensators are not without downsides, however. The shooter, gun crew, or close bystanders may perceive an increase in sound pressure level as well as an increase in muzzle blast and lead exposure. This occurs because the sound, flash, pressure waves, and lead loaded smoke plume normally projected away from the shooter are now partially redirected outwards to the side or sometimes at partially backward angles towards the shooter or gun crew. Standard eye and ear protection, important for all shooters, may not be adequate to avoid hearing damage with the muzzle blast partially vectored back towards the gun crew or spotters by arrowhead shaped reactive muzzle brakes found on sniper team fired anti-materiel rifles like the Barrett M82.
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. 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 in their measured attenuation, ranging from 20 dB to 30 dB, depending on whether they are properly used. Using both ear muffs (whether passive or active) and ear plugs simultaneously results in maximum protection, but the efficacy of such combined protection relative to preventing permanent ear damage is inconclusive, 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(A) protection against a 160 dB(A) noise level. 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.
Brakes and compensators also add length, diameter, and mass to the muzzle end of a firearm, where it will most influence its handling.
Interference with Accuracy 
Brakes and compensators may interfere with accuracy. The problem is particularly pronounced when armour-piercing fin-stabilized discarding-sabot (APFSDS), a type of long-rod penetrator (LRP) are used. Since these APFSDS rounds are the most common armour-piercing ammunition currently, virtually no modern main battle tank guns have muzzle brakes.
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, not to mention posing a hazard to individuals without eye protection. 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.
The redirection of larger amounts escaping high pressure gas can cause discomfort caused by blast-induced sinus cavity concussion. Such discomfort can especially become a problem for anti-materiel rifle shooters due to the bigger than normal cartridges with accompanying large case capacities and propellant volumes these rifles use and can be a reason for promoting accelerated shooter fatigue and flinching. Furthermore the redirected blast generates pressure waves inside the eyeball thus leading to retina ablation when intense battle shooting is performed with AM-guns and large calibers like .50 BMG.
In some African jurisdictions where big game hunting is commonplace, rifles (typically firing powerful loads) equipped with muzzle brakes are banned due to hearing damage hazard to scouts and guides without hearing protection.
See also 
- Muzzle brake in the NRA Firearms Glossary
- STI article on Limcat Undergas Bypass Turbo System recoil compensator
- "SAAMI Glossary, Compensator".
- "Definition for "compensator"". MidwayUSA GunTec Dictionary.
- "Jump Is Taken Out Of Guns By Cylinders On Muzzle" Popular Mechanics, August 1932
- LeVang linear compensator
- Mag-Na-Port handgun porting information
- A muzzle brake manufacturer on pros and cons and recoil reduction of muzzle brakes
- PGRS-1 muzzle brake article
- Summary of a Finnish government report (1992) on silencers, muzzle brakes and noise levels
- (German) and (English) Schalldämpfer = Gehörschützer für Jäger, data collected on noise levels
- Hearing Protection Basics
- Peltor Active Muffs data sheet
- Finnish Research paper
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