Internal Ballistics and Muzzle Attachments - lect 16

Presentations Reminder Before Module Content

• Need to be working and engaging with teams to put presentations together.

• Presentations are coming up soon, so preparation and practice are essential.

Internal Ballistics Review

• Last lecture covered the end of internal ballistics, focusing on processes inside a firearm.

• Understanding these processes can lead to various investigation avenues.

• The pressure-time curve was discussed, explaining pressure changes within the chamber during the three phases of internal ballistics: lock time, ignition time, and barrel time.

Forces Acting Down the Barrel - Example Calculation

Example Scenario

• To illustrate the significant forces and accelerations within a firearm:

  • Consider a 5.56 mm bullet with a mass of 3.6 grams.

  • The bullet is propelled from rest to 1,200 meters per second (high velocity) along a 0.5-meter barrel.

Processes Described

• Ignition of propellants produces gas, creating pressure.

• This pressure applies force to the projectile, causing acceleration down the barrel.

• The bullet also spins for gyroscopic stability.

Applying SUVAT Equations

• Using the SUVAT equation to calculate acceleration:

  • v^2 = u^2 + 2as can be rearranged to find acceleration:

  • a = \frac{v^2 - u^2}{2s}

  • Where:

    • v = final velocity (1,200 m/s)

    • u = initial velocity (0 m/s)

    • a = acceleration

    • s = distance (0.5 m)

Calculation and Results

• Plugging in the values:

  • a = \frac{1200^2 - 0^2}{2 \times 0.5} = 1,440,000 \text{ m/s}^2

• The acceleration inside the barrel is approximately 1,440,000 meters per second squared.

Significance of Acceleration

• The acceleration is huge, approximately 140,000 times greater than the acceleration due to gravity (approximately 10 m/s²).

• This highlights the immense forces at play.

Force Calculation

• Using Newton's second law to calculate force:

  • F = ma

  • Where:

    • F = force

    • m = mass (0.0036 kg)

    • a = acceleration (1,440,000 m/s²)

• Plugging in the values:

  • F = 0.0036 \times 1440000 = 5,184 \text{ N}

• The force is approximately 5,184 Newtons.

Comparison and Conclusions

• The force experienced by the bullet is thousands of Newtons, compared to fractions of a Newton in wind tunnel experiments.

• Bullets withstand these forces due to their design.

Relation to Air Weapon Systems

• Applying internal ballistics principles to air weapon systems.

• Air weapons are common in the UK due to lower legal restrictions. Investigation and understanding are still important.

• Key phases (lock, ignition, barrel time) can be related to air weapon operations, even without traditional ignition.

Propulsion Mechanisms

1. Spring-operated: Compressing a spring releases energy to compress air, launching the projectile.

2. Pre-charged pneumatic (PCP): Uses a pre-pressurized air source (like a diving bottle) to propel the pellet.

Spring-Operated Air Weapons

• Trigger releases a compressed spring instead of activating a primer (no primer in air weapons).

• Lock Time: The time from trigger pull to releasing the compressed spring (different definition than in live fire weapons).

• The compressed spring pushes a piston, compressing air into the barrel, which drives the projectile.

• Compression Time: Equivalent to ignition time. This is the time it takes to compress air to move the pellet.

• Barrel Time: Remains the same (time from projectile movement to exiting the barrel).

Adaptability of Concepts

• General concepts of internal ballistics can be adapted to various weapon systems.

• Understanding and adaptability are key to effective investigation.

• Safety is crucial: Maintain air weapons to prevent air leaks or mechanical failures.

• Compressed air can be dangerous; mechanical mechanisms can also cause injuries if not handled carefully.

• Personal anecdote: A childhood injury with an airgun due to improper handling.

Pre-Charged Pneumatic (PCP) Air Weapons

• Uses gas from an external source (divers bottle, foot pump, or pre-charged CO2 cartridge).

• Operating pressures are high (about 200 times atmospheric pressure).

• A valve system regulates the release of air to launch the projectile.

• Lock Time: Time from trigger pull to valve activation.

• Valve Operation Time: Equivalent to ignition time; the time for the valve to open and air to propel the projectile. No ignition time, instead valve operation time applies.

• Barrel Time: Remains the same (time projectile spends in the barrel while in motion).

Breaking Down Phases for Investigation

• Three phases of investigation:

  1. Lock Time: Identify mechanical issues from trigger to activation.

  2. Ignition/Valve Operation: Check for problems in air compression or valve systems.

  3. Barrel Time: Look for barrel blockages, wear, or issues with projectile rotation.

• This methodical approach helps manage and troubleshoot weapon system problems.

Air Weapons and Legal Classifications

• Kinetic energy of the projectile determines legal status:

  • Air rifles below 12 foot-pounds (approximately 16 joules) are generally unlicensed.

    • Remmber that air pistols have half this value.

  • Air pistols below 8 joules have a different value.

• Above these limits:

  • Air rifles become Section 1 firearms (require a firearm certificate if over 16 joules).

  • Air pistols can become Section 5 prohibited weapons (if is in excess of eight joules), leading to potential jail time without proper certification.

• Important to avoid modifying air weapons to increase energy output, which can lead to severe legal consequences.

Testing Energy Output

• The "Home Office test" involves firing air weapons through a chronograph to measure velocities and calculate energy output.

• Kinetic energy is related to mass and velocity ($\frac{1}{2}mv^2), use a range of different airgun pellet designs or masses in particular.

• Varying masses of pellets are used (heavy, medium, light) to see how energy output balances between mass and velocity.

• Ten shots of each mass are fired, and velocities are recorded.

• Individual kinetic energies are calculated for each shot, and the results are not averaged.

• The important calculation being: KE = \frac{1}{2} m v^2

• The highest single-shot energy determines the weapon's classification.

Legal Considerations

• It can be difficult if a new projectile comes on the market, and the weapon is capable of going above that legal limit, so you should be aware of the classification of air weapons.

• Ignorance can be argued in court in some cases, especially if new projectiles on the market exceed legal limits post-purchase, but legal arguments may be necessary if there are penalties.

Hand Loading

• Hand loaders are those who make their own ammunition, for example professional target shooters, who want their ammunition a specific way.

• They tailor propellant loads and mixtures for specific ballistic outputs.

• Skilled hand loaders can produce more consistent ammunition than factory loads.

• Training courses are essential to understand the process and ensure safety.

Risks

• Poorly considered loads can lead to:

  • Pressure chambers exceeding design limits, causing the weapon to explode.

  • Too low ignition pressure (squib loads), where the bullet jams in the barrel.

  • A second shot fired into a jammed barrel can cause the weapon to explode.

• Specific training and practice are necessary.

Safety Advice

• Never use ammunition that someone else has hand-loaded.

• You can't know the exact load or process used. Factory ammunition is generally consistent and safer.

Muzzle Attachments

• The new topic is muzzle attachments.

• It include accessories placed on the end of the barrel to modify ballistic output (sound, flash, etc.).

• Knowledge and safe usage are crucial, as different attachments are designed for different purposes and ammunition types.

• Accessories designed to diminish noise or flash are legally considered firearms in their own right and often classified in the same class as the weapon.

Muzzle Condition

• The end of the barrel (muzzle) must be in good condition.

• Damage can cause serious issues with ammunition and accuracy.

• Dropping or scraping the gun can damage the muzzle crown (the very end of the muzzle).

Muzzle Crown

• The muzzle crown is the surface at the end of the barrel.

• Damage, even tiny scuffs, can cause particles of metal to stick into the bullet's path.

• This can cause instability and tumbling, leading to dangerous and unpredictable trajectories.

• Maintenance is essential; carefully remove any damage to ensure a clean bullet path.

Sound Suppressors Overview

• The lecture covers sound suppressors, often incorrectly called silencers.

• The key sounds from a firearm, listed from loudest to quietest, typically include:

  1. Pressure waves (supersonic gases and bullets)

  2. Mechanical action noises

  3. Air friction

  4. Impact sound

Pressure Waves

• Caused by components going supersonic (similar to a sonic boom).

• Supersonic Gases: Gases expanding rapidly create a loud crack.

• Sound suppressors attempt to slow these gases to subsonic speeds.

• Supersonic Bullets: Bullets exceeding the speed of sound also create a crack.

• Sound suppressors can't eliminate this sound.

Sound Suppressors and Ammunition

• Supersonic Ammunition: Sound suppressors are not very effective because bullets create their own sonic boom.

• Subsonic Ammunition: Designed to stay below approximately 340-350 m/s (the speed of sound).

• When combined with a suppressor, significant sound reduction occurs because there are no supersonic cracks.

Other Noises

• Mechanical Action Noises: Significant in machine guns but less relevant with suppressors.

• Air Friction: Relatively quiet.

• Impact Sound: Depends on the target material (can vary from quiet to very loud).

Implications of Subsonic Velocities

• Subsonic bullets have shorter ranges and altered trajectories.

• Best suited for close-range combat.

Factors that Vary Speed of Sound in Air

• The speed of sound in air varies with environmental conditions, especially temperature.

• The speed of sound can be determined by this equation: 331.3 + 0.606*T, with T being the temperature in Celsius.

Sound Suppressor Effectiveness

• A suppressor can only reduce the supersonic pressure wave caused by rapidly expanding gases.

• Integral Sound Suppressors: Built into or permanently attached to the barrel.

• Interchangeable Sound Suppressors: Can be added or removed.

• Attachments: Screw-on, bayonet fitting, or grub screw.

Usage

• Relatively ineffective with supersonic ammo.

• Highly effective with subsonic ammo.

How Sound Suppressors Work

• Gases expand rapidly when the bullet exits the barrel, producing the supersonic crack.

• The suppressor's purpose is to reduce the energy and velocity of these gases before they exit.

• Turbulence: Increase air turbulence using controlled chambers.

Expansion and Turbulence

• Gases bounce around inside the barrel. Extra chambers cause the gases to hit surfaces.

• Energy Transfer: Each impact transfers energy to the surface, reducing the velocity of the gases.

• The goal is to reduce the gas velocity below the speed of sound. Expansion chambers allow more expansion and turbulence.

Key Components

• Expansion chambers and baffles: Expansion chambers provides more space. Baffles interact with the propulsion gas behind the projectile.

Sound Suppressor Designs

Main Four Types:

1. Can: A hollow extension on the muzzle.

2. Baffle: A can with horizontal partitions (baffles) inside.

3. Reflex: More complex baffles creating expansion chambers.

4. Active: Baffles are spring-loaded. Reflex suppressors have fixed baffles, while these baffles have a more elastic movement that gives an added effect.

Designs of Sound Suppressors

• A Can: Hollow with no internal structures.

• A Baffle: Horizontal partitions cause gases to bounce around.

• A Reflex: Complex expansion chambers for more interactions.

• An Active: Spring-loaded baffles absorb energy from gases.

Presentations Reminder Before Module Content

• Engaging with teams is crucial for effective presentations.

• Presentations are imminent, so thorough preparation and consistent practice are vital for success.

Internal Ballistics Review

• The previous lecture concluded the discussion on internal ballistics, emphasizing processes within a firearm from trigger pull to projectile exit.

• A comprehensive grasp of these processes is essential for forensic investigations, accident reconstructions, and firearm performance analysis.

• The pressure-time curve illustrates pressure dynamics within the chamber during three key phases: lock time, ignition time, and barrel time. Understanding these phases helps diagnose firearm malfunctions and assess ammunition performance.

Forces Acting Down the Barrel - Example Calculation

Example Scenario

• Detailed analysis of forces and accelerations within a firearm using a specific example:

  • Consider a 5.56 mm bullet weighing 3.6 grams.

  • The bullet accelerates from rest to 1,200 meters per second within a 0.5-meter barrel.

Processes Described

• Ignition of propellant generates high-pressure gas.

• This pressure exerts force on the projectile, accelerating it down the barrel.

• The bullet also experiences spin, enhancing gyroscopic stability, which is critical for accuracy.

Applying SUVAT Equations

• Using the SUVAT equation to determine acceleration:

  • v^2 = u^2 + 2as can be rearranged to solve for acceleration:

  • a = Rac{v^2 - u^2}{2s}

  • Where:

    • v = final velocity (1,200 m/s)

    • u = initial velocity (0 m/s)

    • a = acceleration

    • s = distance (0.5 m)

Calculation and Results

• Substituting values into the equation:

  • a = Rac{1200^2 - 0^2}{2 Imes 0.5} = 1,440,000 Ext{ m/s}^2

• The calculated acceleration inside the barrel is approximately 1,440,000 meters per second squared.

Significance of Acceleration

• This immense acceleration is approximately 140,000 times greater than gravitational acceleration (approximately 10 m/s²).

• This underscores the extreme forces involved in firearm operation.

Force Calculation

• Applying Newton's second law to calculate force:

  • F = ma

  • Where:

    • F = force

    • m = mass (0.0036 kg)

    • a = acceleration (1,440,000 m/s²)

• Plugging in the values:

  • F = 0.0036 Imes 1440000 = 5,184 Ext{ N}

• The calculated force is approximately 5,184 Newtons.

Comparison and Conclusions

• The bullet experiences forces of thousands of Newtons inside the barrel, contrasting sharply with wind tunnel experiments where forces are fractions of a Newton.

• This calculation highlights the importance of bullet design to withstand such extreme conditions.

Relation to Air Weapon Systems

• Applying internal ballistics principles to air weapon systems, noting their relevance in forensic and legal contexts.

• Air weapons are prevalent in the UK due to relaxed regulations compared to firearms.

• Understanding internal ballistics principles is still crucial for investigations involving air weapons.

• The key phases (lock, ignition, barrel time) can be adapted to describe air weapon operation, albeit without traditional ignition processes.

Propulsion Mechanisms

1. Spring-operated: A compressed spring releases energy to compress air, which then propels the projectile.

2. Pre-charged pneumatic (PCP): Uses a pre-pressurized air source to launch the pellet, offering consistent power and minimal recoil.

Spring-Operated Air Weapons

• A trigger releases a compressed spring instead of a primer.

• Lock Time: The duration from trigger pull to the release of the compressed spring.

• The released spring drives a piston, compressing air within the barrel to propel the projectile.

• Compression Time: Equivalent to ignition time; describes the duration to compress air and initiate pellet movement.

• Barrel Time: The time the projectile spends moving through the barrel until exit remains consistent.

Adaptability of Concepts

• Basic principles of internal ballistics are applicable across various weapon systems.

• Comprehensive understanding and adaptability are essential for forensic investigations and safety.

• Safety is paramount; maintain air weapons to prevent air leaks and mechanical failures.

• Compressed air poses risks; mechanical mechanisms can cause injuries if mishandled. Regular maintenance and adherence to safety protocols are crucial.

• Personal safety anecdote emphasizing the importance of proper handling.

Pre-Charged Pneumatic (PCP) Air Weapons

• Uses externally sourced gas (diving bottles, foot pumps, CO2 cartridges).

• High operating pressures (around 200 times atmospheric pressure) ensure powerful and consistent shots.

• A valve regulates air release to launch the projectile efficiently.

• Lock Time: The time from trigger pull to valve activation, influencing shot timing and accuracy.

• Valve Operation Time: Equivalent to ignition time in firearms; describes the duration for the valve to open and propel the projectile.

• Barrel Time: Remains the same, measuring projectile travel time within the barrel.

Breaking Down Phases for Investigation

• Methodical approach to investigate air weapon incidents:

  1. Lock Time: Examine mechanical components from trigger to activation to identify issues.

  2. Ignition/Valve Operation: Check air compression and valve systems for malfunctions affecting performance.

  3. Barrel Time: Inspect the barrel for blockages, wear, and projectile rotation issues to ensure accuracy.

• This structured approach aids effective troubleshooting and forensic analysis.

Air Weapons and Legal Classifications

• Legal status depends on kinetic energy:

  • Air rifles below 12 foot-pounds (approximately 16 joules) are generally unlicensed, allowing for recreational use without strict regulation.

  • Air pistols have a different legal limit.

• Above these limits:

  • Air rifles become Section 1 firearms (require a firearm certificate), resulting in stringent control and monitoring.

  • Air pistols can become Section 5 prohibited weapons, leading to severe penalties, including imprisonment, without proper authorization.

• Modifying air weapons to increase energy output can lead to serious legal repercussions.

Testing Energy Output

• The "Home Office test" measures velocity using a chronograph to calculate energy output, ensuring compliance with legal standards.

• Kinetic energy is related to mass and velocity (\fRac{1}{2}mv^2), so various pellet masses are used.

• Heavy, medium, and light pellets are tested to observe the balance between mass and velocity.

• Ten shots per mass are recorded, with individual kinetic energies calculated (not averaged).

• The highest single-shot energy determines the weapon's legal classification.

Legal Considerations

• New projectiles exceeding legal limits can pose classification challenges.

• Ignorance may be a defense, especially with new projectiles, but legal arguments may be necessary.

Hand Loading

• Hand loaders customize ammunition for specific ballistic performance, often favored by target shooters.

• They carefully adjust propellant loads and mixtures to achieve desired outputs.

• Skilled hand loaders can create more consistent ammunition than factory-produced rounds, enhancing accuracy.

• Formal training is essential for safety and understanding the hand-loading process.

Risks

• Poorly considered loads can cause:

  • The pressure chamber to exceed design limits, leading to weapon explosion and potential injury.

  • Too low ignition pressure (squib loads), resulting in the bullet lodging in the barrel.

  • Firing a second shot into a barrel with a lodged bullet can cause catastrophic failure.

• Specific training and meticulous practice are crucial to avoid these hazards.

Safety Advice

• Do not use ammunition hand-loaded by others.

• The exact load and process are unknown, increasing risk. Factory ammunition is safer and more consistent.

Muzzle Attachments

• Muzzle attachments are accessories added to the barrel's end to alter ballistic output (sound, flash, recoil).

• Knowledge and safe usage are vital, as attachments vary for different purposes and ammunition types.

• Accessories that reduce noise or flash are legally considered firearms and regulated accordingly.

Muzzle Condition

• The muzzle must be in good condition to ensure accuracy and safety.

• Damage can affect ammunition performance and trajectory.

• Dropping or scraping the gun may damage the muzzle crown.

Muzzle Crown

• The muzzle crown is the surface at the barrel's end.

• Damage, including small scuffs, can cause metal particles to interfere with the bullet's path.

• This interference can lead to instability and unpredictable trajectories.

• Regular maintenance is essential to ensure a clean bullet path.

Sound Suppressors Overview

• Discussion on sound suppressors, commonly known as silencers, and their function.

• Key firearm sounds (loudest to quietest):

  1. Pressure waves (supersonic gases and bullets)

  2. Mechanical action noises

  3. Air friction

  4. Impact sound

Pressure Waves

• Pressure waves are caused by components exceeding the speed of sound.

• Supersonic Gases: Rapidly expanding gases create a loud crack, which suppressors aim to mitigate by reducing gas velocity.

• Supersonic Bullets: Bullets faster than sound generate a sonic boom, which suppressors cannot eliminate.

Sound Suppressors and Ammunition

• Supersonic Ammunition: Suppressors are less effective because the bullet's sonic boom dominates the sound profile.

• Subsonic Ammunition: Designed to remain below the speed of sound (approximately 340-350 m/s).

• Combining suppressors with subsonic ammunition substantially reduces noise by eliminating supersonic cracks.

Other Noises

• Mechanical Action Noises: Significant in automatic weapons but less so with suppressors.

• Air Friction: Relatively quiet and less of a concern.

• Impact Sound: Varies depending on the target material and is not affected by suppressors.

Implications of Subsonic Velocities

• Subsonic bullets have reduced range and altered trajectories, affecting their suitability.

• Best suited for close-range scenarios where stealth is more important than long-range accuracy.

Factors that Vary Speed of Sound in Air

• The speed of sound varies with environmental factors, especially temperature.

• The speed of sound can be approximated by the equation: 331.3 + 0.606*T, where T$$ is the temperature in Celsius.

Sound Suppressor Effectiveness

• Suppressors primarily reduce supersonic pressure waves from rapidly expanding gases.

• Integral Sound Suppressors: Built into the barrel for maximum sound reduction.

• Interchangeable Sound Suppressors: Offer flexibility and can be added or removed easily.

• Attachments: Common methods include screw-on, bayonet fitting, and grub screw mechanisms.

Usage

• Relatively ineffective with supersonic ammunition because the bullet itself creates a sonic boom.

• Highly effective with subsonic ammunition by minimizing the noise from expanding gases.

How Sound Suppressors Work

• Suppressors reduce gas energy and velocity before exiting the barrel, mitigating noise.

• Turbulence: Controlled chambers increase air turbulence to slow gases.

Expansion and Turbulence

• Gases bounce within the suppressor, impacting surfaces and transferring energy to reduce velocity.

• Expansion chambers and baffles facilitate turbulence, reducing gas velocity below the speed of sound.

Key Components

• Expansion chambers provide extra space, while baffles interact with propellant gases.

Sound Suppressor Designs