How Muzzle Blast Occurs in RIFLE

 

Muzzle Blast

Hi guys thanks for tunning here, let us see about how the muzzle blast happens when the gun is fired.

a)     Gas Expansion: The burning gunpowder rapidly converts to gas, creating a high-pressure environment inside the cartridge case.

 

b)     Bullet Movement: The expanding gases push the bullet out of the cartridge case and down the barrel. The bullet is forced through the rifling of the barrel, which imparts a spin to stabilize it in flight.

 

 

c)     Muzzle Blast: As the bullet exists the barrel, the high-pressure gases following it rapidly expand into the lower pressure atmosphere, creating a muzzle blast is responsible for the loud noise and visible flash associated with firing.

 

d)     Rapid Expansion: The gases that were previously contained and pressurized with in the barrel now expand rapidly into the surrounding atmosphere, which is at a much lower pressure.

 

 

e)     Shock Wave Creation: The sudden release of these high-pressure gases in to the atmosphere creates a shockwave. This shock wave is essentially a rapid compression and subsequent expansion of air molecules, which produces the loud sound of the gunshot.

How Rapid Expansion and Shockwave are Created?

a)     High Pressure Gas Generation:

·       Combustion: When the gunpowder in the cartridge burns, it generates hot gases under high pressure.

·       Confined Space: These gases are initially confined with in the cartridge and barrel, causing the pressure to increase significantly.

b)    Bullet Propulsion:

·       Pressure Gradient: The high-pressure gases push the bullet down the barrel, following the path of least resistance.

·       Barrel Exit: As the bullet exits the barrel, it leaves an open pathway for the gases to escape.

c)     Gas Release:

·       Pressure Drop: The sudden release of gases from the high-pressure environment of the barrel to the lower pressure environment of the atmosphere causes the gases to expand rapidly.

·       Volume Expansion: The gases occupy a much larger volume almost instantaneously as they escape the atmosphere.

Shock Wave Creation:

a)     Super sonic Flow:

·       Gas Velocity: The escaping gases can exceed the speed of sound due to the high-pressure differential and the narrow passage of the barrel opening.

·       Mach Disc Formation: As the gases move at supersonic speeds, they form a shockwave known as a MACH Disc or shock diamond just outside the muzzle.

b)    Shock Wave Propagation:

·       Compression Wave: The rapid expansion of gases creates a compression wave in the air. This wave travels faster than the speed of sound, forming a shock wave.

·       Overpressure: The shockwave is characterized by a sudden spike in pressure or over pressure followed by a rapid drop, which is perceived as loud bang.

c)     Interaction with Atmosphere:

·       Sound Wave: The shockwave propagates through the atmosphere as a sound wave. The high-pressure front moves outward compressing air molecules in its path.

d)    Overexpansion and Under expansion:

·       As the supersonic gases exit the muzzle, they initially expand and their pressure drops below atmospheric pressure (overexpansion).

·       The surrounding atmospheric pressure then compresses the flow, causing it to increase in pressure again (Under expansion)

·       This cycle of overexpansion and under expansion creates a series of shockwaves and expansion fans.

·       The shockwaves are compression waves where the gas pressure and density suddenly increase.

·       The expansion fans are areas where the gas pressure and density suddenly decrease.

e)     Shock Diamonds:

·       The interaction between these shockwaves and expansion fans forms a pattern of diamond shaped regions of alternating high and low pressure and temperature.

·       These are visible as bright spots in the exhaust plume, known as Mach discs or shock diamonds.

Compression of Air Molecules by a Shock Wave:

a)     Supersonic Expansion:

·       The expanding gases move at supersonic speeds, leading to a steep pressure gradient at the shock front.

·       This shock front compresses the air in front of it because the air molecules cannot move out of the wat quickly enough.

b)    Sudden Compression:

·       The shock wave forces air molecules closer together, increasing their density and pressure, the compression also raises the temperature of the air due to the increase in kinetic energy of the air molecules increases due to the compression.

c)     Compression Process:

·       The air molecules are forced closer together, increasing the local air pressure.

·       This compression results in a rapid rise in temperature because the kinetic energy of the moving air molecules increases.

·       The density of the air also increases as the molecules are packed more tightly together.

d)    Energy Dissipation:

·       The energy of the shock wave dissipates over distance due to the spread of the wavefront and interactions with air molecules.

·       As the shock wave loses energy, the intensity of the compression decreases.

e)     Natural Tendency to Equalize pressure:

·       Gases naturally move from regions of high pressure to regions of lower pressure to equalize the pressure difference.

·       The compressed air behind the shock wave expands outward into the surrounding lower pressure air, reducing its pressure and density.

Energy Dissipation of the Shock Wave:

a)     Spread of the Wavefront:

·       As the shock wave moves away from its source, the wavefront spreads out, the energy in the shock wave is distributed over a larger volume of air, reducing the energy density.

b)    Viscous Effects:

·       The movement of the shock wave through the air involves interactions between air molecules, which create friction and heat.

·       These viscous effects dissipate some of the shock waves energy as thermal energy, reducing the intensity of the wave.

c)     Thermodynamic Processes:

·       The compression and subsequent expansion of air involve thermodynamic processes where some energy is lost as heat.

·       This conversion of mechanical energy to thermal energy results in a decrease in the shock waves overall energy.

d)    Wave Attenuation:

·       As the shock wave travels further, it encounters more air resistance, which attenuates (weakens) the wave.

·       The sharp pressure gradient of the shock wave become less pronounced, and the wave transitions to more normal sound wave over time.

e)     Turbulence and Mixing:

·       The shock wave can create turbulence in the air, causing mixing of high pressure and low-pressure regions.

·       This turbulent mixing further dissipates energy, contributing to the weakening of the shock wave.

Detailed Steps of Expansion:

a)     Immediate Post shock Region:

·       Directly behind the high-pressure front of the shock wave, there is a region where the air has been compressed and heated.

·       This region is followed by a rapid expansion as the energy begins to dissipate.

b)    Rarefaction Wave:

·       Following the shock wave is a rarefaction wave, which is a region where the pressure, temperature, and density decrease.

·       The rarefaction wave represents the air molecules returning to a more normal state after being compressed.

c)     Gradual Pressure Drop:

·       The high-pressure air begins to expand into the surrounding lower pressure air.

·       This expansion is driven by the natural tendency of gases to move form regions of high pressure to regions of low pressure.

d)    Spread of the Wavefront:

·       As the shock wave travels further from the source, the wavefront spreads out.

·       The energy of the shock wave is distributed over a large area, reducing the pressure difference between the compressed region and the surrounding air.

Reflection of Shock Waves:

a)     Muzzle Blast:

·       When a bullet exits the muzzle, high pressure gases from the combustion of gunpowder are rapidly expelled into the lower pressure atmosphere.

·       This rapid expansion generates a primary shock wave that propagates outward form the muzzle into the low-pressure environment.

b)    Formation of Contact or Boundary Surface:

·       The high pressure, high temperature gases create a contact surface with the lower pressure ambient air.

·       This interface marks the boundary between the density, expanding gas and the less density surrounding atmosphere.

c)     Initial Shock Wave Propagation:

·       The initial shock wave moves outward into the lower pressure region, compressing and heating the air as it travels, mentioned above.

d)    Reflection of Shock Waves:

·       When the shock wave encounters surface such as the ground, nearby objects, or event the muzzle itself, it can reflect back into the expanding gas.

·       These reflected shock waves interact with the original shock wave and the expanding gas, creating complex wave patterns.

e)     Secondary Shock Waves and Interference:

·       The reflected shock waves can cause secondary compression of the gas, leading to additional pressure increases and further interactions with in the expanding gas cloud.

·       The results in interference patterns where the waves overlap, creating regions of constructive and destructive interference.

 

How the Bang Sound is Produced:

a)     Bang Sound:

·       The rapid pressure change as the shock wave passes an observer’s ears is perceived as a loud bang.

·       The sharp rise and fall in pressure with in a very short time frame produce the characteristic gunshot sound.

b)    Echoes and Reflections:

·       The shock wave can reflect off surfaces like walls, buildings, and terrain, creating echoes.

·       Multiple reflection can cause a series of delayed sounds following the initial bang. And the below figure shows the Shock Waves Graph.