A muzzle brake or recoil compensator is a device connected to the muzzle of a firearm or cannon that redirects propellant gases to counter recoil and unwanted rising of the barrel during rapid fire. The concept was introduced for artillery and was a common feature on many anti-tank guns, especially those in tanks, in order to reduce the area needed to take up the recoil stroke. They have been used in various forms for rifles and pistols to help control recoil and the rising of the barrel that normally occurs after firing. They are used on pistols for practical pistol competitions, and are usually called compensators in this context.
The interchangeable terms muzzle rise, muzzle flip, or muzzle climb refer to the tendency of a firearm's front end (the muzzle end of the barrel) to rise after firing. Firearms with less height from the grip line to the barrel centerline tend to experience less muzzle rise.
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 reactive forces from the fired bullet and 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 makes the firearm rotate and the muzzle end 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.
Design and construction
Muzzle brakes are simple in concept, such as the one employed on the 90 mm M3 gun 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 gasses that follows the departure of a projectile. Since these gasses are the primary means by which the sound of the blast initially propagates, all muzzle brakes also redirect the sound of the blast to some degree, making it louder in the direction(s) the gasses are directed towards and softer in other directions.
All muzzle brake designs share a basic principle: they partially divert combustion gases at a generally sideways angle, away from the muzzle end of the bore. The angle the gasses are directed towards fundamentally affects how the brake behaves. Any brake which is attached to the end of the muzzle will also add mass, increasing its inertia and moving its center of mass forward; the former will reduce recoil, and the latter will reduce muzzle rise when not in zero-g conditions. Such brakes also add surface area to the muzzle (usually more than just their length would imply, as they are also wider than the original muzzle), improving their ability to dissipate heat, which reduces the velocity of escaping gasses. Since all brakes reduce the surface area of the escaping gasses at the time they leave the barrel, they all also reduce any increase in combustion which would otherwise suddenly occur there (typically only the case when the barrel is not long enough for the propellant to fully burn), reducing muzzle flash and recoil if so. Likewise, any brake which allows the gasses to expand prior to exiting has the same effect; such brakes are also, by definition, suppressors.
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 also angles 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 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.
Most linear compensators redirect the gases forward. Since that is where the bullet is going, they typically work by allowing the gases to expand into the compensator, which surrounds the muzzle but only has holes facing forward; like any device which allows the gases to expand before leaving the firearm; they are effectively a type of muzzle shroud. They reduce muzzle rise similarly to the mechanism by which a sideways brake does: since all the gas is escaping in the same direction, any muzzle rise would need to alter the velocity of the gas, which costs kinetic energy. They actually add to recoil, since any gases redirected forwards impart more recoil force back into the shooter, and need to compensate for recoil via other methods (such as those universal to all brakes). When the brake redirects the gases directly backwards, instead, the effect is similar to the reverse thrust system on an aircraft jet engine; any blast energy coming back at the shooter is pushing "against" the recoil, effectively reducing the actual amount of recoil on the shooter. Of course, this also means the gases are directed towards the shooter.
Brakes with vent left and right reduce twist, since they give the vented gas a more specific velocity when escaping the firearm perpendicular to the ballistic motion (rather than every direction), and have gas vent through a part of the firearm, the net effect of which is that twisting the firearm during the shot would change the velocity of the escaping gases, unlike a brakeless muzzle, where twist would have no effect, as velocity includes direction. They reduce rise in a similar fashion.
When the primary direction the gases are redirected upward, the braking is referred to as porting. Porting typically involves precision-drilled ports or holes in the forward dorsal part of the barrel (and slide on pistols and shotguns). These holes 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 rise. The concept applies Newton's third law: the exhaust directed upward causes a reciprocal force downward. This is why firearms are virtually never ported on the bottom of the barrel, as that would primarily serve to exacerbate muzzle rise, rather than mitigate it. Even single shots of magnum-strength loads are uncomfortable for all but the most seasoned shooters. Porting has the generally undesired consequence of shortening the effective barrel length, reducing muzzle velocity, where a regular muzzle brake is an extension added to the barrel, and does not reduce muzzle velocities. Porting has obvious advantages for faster follow-up shots, especially for 3-round burst operation.
Though there are numerous ways to measure 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 lets a shooter realign a weapon's sights 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 lets the shooter 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 must 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.
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.
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 most influences its handling and may interfere with accuracy as muzzle rise will occur when the brake is removed and shooting without the brake can throw off the strike of the round.
Another problem can occur when saboted ammunition is used as the sabot tends to break up inside the brake. 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 may direct pressure waves toward the eye, potentially leading to retinal detachment when repeated shooting is performed with anti-materiel and large caliber weapons.
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