Muzzle blast

 ( Shock Waves ) 

A muzzle blast is an explosive shockwave created at the muzzle of a firearm during shooting. Before a projectile leaves the gun barrel, it the bore and "plugs up" the pressurized gaseous products of the propellant combustion behind it, essentially containing the gases within a closed system as a neutral element in the overall momentum of the system's physics. However, when the projectile exits the barrel, this functional seal is removed and the highly energetic bore gases are suddenly free to exit the muzzle and rapidly expand in the form of a supersonic shockwave (which can often be fast enough to momentarily overtake the projectile and affect its flight dynamics), thus creating the muzzle blast.

The muzzle blast is often broken down into two components: an auditory component Muzzle Blast Sound Intensity, Firearm Sound Pressure Level and a non-auditory component. Blast Overpressure Studies. Nonauditory Damage Risk Assessment for Simulated Muzzle Blast from a l2Omm Ml2l Mortar System. (abstract) The auditory component is the loud "Bang!" sound of the gunshot, and is important because it can cause significant hearing loss to surrounding personnel and also give away the gun's position. The non-auditory component is the infrasonic compression wave, and can cause concussive damage to nearby items.

In addition to the blast itself, some of the gases' energy is also released as light energy, known as a muzzle flash.

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Components

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Gun sound The audible sound of a gun discharging, also known as the muzzle report or gunfire, may have two sources: the muzzle blast itself, which manifests as a loud and brief "pop" or "bang", and any sonic boom produced by a transonic or supersonic projectile, which manifest as a sharp whipcracking that persists a bit longer. The muzzle blast is by far the main component of a gunfire, due to the intensity of sound energy released and the proximity to the shooter and bystanders. Muzzle blasts can easily exceed sound pressure levels of 140 , which can rupture eardrums and cause permanent sensorineural hearing loss even with brief and infrequent exposure. Hearing protection FAQ With large guns with much higher muzzle energy, for instance artillery, that danger can extend outwards a significant distance from the muzzle, Prediction of Standoff Distances to Prevent Loss of Hearing from Muzzle Blast which mandates wearing of hearing protections for all personnel in proximity for occupational health purposes.

For , help to reduce the muzzle report of firearms by providing a larger area for the propellant gas to expand, decelerate and cool before releasing sound energy into the surrounding. Other muzzle devices such as muzzle shroud can also protect hearing by deflecting the pressure wave forward and away from the shooter and bystanders. Recoil-reducing devices such as however worsen potential hearing damage, as these modulate the muzzle blast by increasing the lateral vectors nearer to the shooter.

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Compression wave The overpressure wave from a firearm's muzzle blast are infrasonic and thus inaudible to human ears, but it still can be highly energy-intense due to the gases expanding at an extremely high velocity. Residual pressures at the muzzle can be a significant fraction of the peak bore pressure, especially when short barrels are used. This energy can also be regulated by a muzzle brake to reduce the recoil of the firearm, or harnessed by a muzzle booster to provide energy to cycle the firearm actions of self-loading firearms.

The force of the muzzle blast can cause shock damage to nearby items around the muzzle, and with artillery, the energy is sufficiently large to cause significant damage to surrounding structures and vehicles. Muzzle Blast Damage to Combat Vehicles (abstract) It is thus important for the gun crew and any nearby friendly troops to stay clear of the potential directions of blast vectors, in order to avoid unnecessary collateral damages.

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Recoil Typically the majority of the blast impulse is vectored to a forward direction, creating a jet propulsion effect that exerts force back upon the barrel, resulting in an additional rearward momentum on top of the reactional momentum generated by the projectile before it exits the gun. The overall recoil applied to the firearm is thus equal and opposite to the total forward momentum of not only the projectile, but also the ejected gas. Likewise, the recoil energy given to the firearm is affected by the ejected gas. By conservation of mass, the mass of the gas will be equal to the original mass of the propellant (assuming complete burning). As a rough approximation, the ejected gas can be considered to have an effective exit velocity of $\backslash alpha\; V\_0$ where $V\_0$ is the muzzle velocity of the projectile and $\backslash alpha$ is approximately constant. The total momentum $p\_e$ of the propellant and projectile will then be:

$p\_e=m\_pV\_0\; +\; m\_g\; \backslash alpha\; V\_0\backslash ,$

where: $m\_g\backslash ,$ is the mass of the propellant charge, equal to the mass of the ejected gas.

This expression should be substituted into the expression for projectile momentum in order to obtain a more accurate description of the recoil process. The effective velocity may be used in the energy equation as well, but since the value of α used is generally specified for the momentum equation, the energy values obtained may be less accurate. The value of the constant α is generally taken to lie between 1.25 and 1.75. It is mostly dependent upon the type of propellant used, but may depend slightly on other things such as the ratio of the length of the barrel to its radius.

Muzzle devices can reduce the recoil impulse by altering the pattern of gas expansion. For instance, primarily works by diverting some of the gas ejecta towards the sides, increasing the lateral blast intensity (hence louder and more concussive to the sides) but reducing the thrust from the forward-projection (thus less recoil), with some designs claiming up to 40-60% reduction in perceived recoil. Similarly, recoil compensators divert the gas ejecta mostly upwards to counteract the muzzle rise. However, work on a different principle, not by vectoring the gas expansion laterally but instead by modulating the forward speed of the gas expansion. By using internal sound baffle, the gas is made to travel through a convoluted path before eventually released outside at the front of the suppressor, thus dissipating its energy over a larger area and a longer time. This reduces both the intensity of the blast (thus lower loudness) and the recoil generated (as for the same impulse, force is inversely proportional to time).

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Detection Muzzle blasts can stir up significant , especially from large-caliber guns when firing low and flat, which can be visible from distance and thus give away the gun's position, increasing the risk of inviting counter-fire. Preventive actions may consist of wetting the soil of the surrounding ground, having the muzzle brake vector to blast up and away from the ground, or covering the area around the muzzle with a tarpaulin to shroud down as much airborne dust as possible.

detect muzzle blast with and triangulate the location where the shots were fired. These are commercially available, and have been installed by law enforcement agencies as in many high-crime rate areas of . They can provide a fairly precise location of the source of a shot fired outdoors — 99% to within or better — and provide the data to police within seconds of a firing.

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See also

• Suppressor
• Muzzle brake
• Recoil compensator
• Muzzle booster
• Muzzle shroud

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