Ballistics - Primers, Propellants, and Powders - lect 18

Housekeeping Notices

• Labs Continuing: Ballistics labs continue this week. Prepare by reading the lab scripts and understanding the tasks.

• Lab Write-Ups: If you attended labs last week, ensure your write-ups are completed or in progress.

• Presentations on Thursday: Finalize group preparations for presentations this Thursday.

  • If there are any issues within the group please respond to the email sent out.

• Slide Upload: Upload presentation slides 24 hours before your presentation slot.

  • This is needed to ensure a smooth transition between groups.

• Jury Duty: Last two court sessions this year on Wednesday afternoon/evening and Thursday late afternoon/early evening.

  • Attend if you still need to fulfill your duty or want additional experience.

Primers and Propellants

• Difference between Primers and Propellants:

  • Primers: Detonate (explode) at supersonic speeds.

  • Propellants: Burn at subsonic speeds (deflagration).

• Deflagration: A subsonic combustion event propagating through thermal conductivity, where each layer heats the next.

• Propellants are designed to deflagrate, not detonate, within the ammunition system.

• Propellants can explode under specific conditions (e.g., high containment).

Types of Propellants

• Historic vs. Modern Propellants

  • Older systems still work and are relevant in understanding potential criminal uses of firearms.

Black Powder

• History: Dates back to before 424 BC, used in pyrotechnics by the Chinese for generating gas to launch projectiles.

• Usage: Historically used in muzzle-loading firearms.

• Modern Usage: Still used in older fire arm reenactments

• Composition:

  • 14\%$ Sulphur

  • 10\%$ Carbon

  • 76\%$ Potassium Nitrate

• Potassium Nitrate: Acts as the fuel driving the explosive reaction; also known as saltpeter and used in fertilizers.

• ANFO (Ammonium Nitrate Fuel Oil): An explosive composition that can sometimes use potassium nitrate instead of ammonium nitrate.

• Black Powder Reaction:

  • 4KNO3(s) + 7C(s) + S(s) \rightarrow 3CO2(g) + N2(g) + K2S(s) + K2CO3(s)

  • Products include carbon dioxide, nitrogen gas, and potassium sulfide (a solid residue).

• Potassium Sulfide:

  • Can cause fouling (residue buildup) in gun barrels.

  • Reacts with water to form sulfuric acid, leading to weapon erosion.

• Mixture Challenges:

  • If not ground to the same particle size, components separate easily due to density differences.

  • Milling is a process of grinding constituents to ensure consistent mixture and performance.

• Ineffective Combustion:

  • Produces partially burned residues and significant smoke (large plumes).

  • Smoke reveals the shooter's position and obstructs their view.

• Fouling:

  • Residues that build up inside the barrel, potentially blocking bullet transit.

  • Regular weapon maintenance is essential.

• Disadvantages:

  • Hygroscopic: Absorbs moisture from the air, leading to toxic byproducts (sulfuric acid).

  • Unstable when hot: Has a low cook-off temperature.

  • Highly sensitive to static electricity.

• Modern Improvements:

  • Enclosed brass cartridge systems prevent water ingress.

  • Brass acts as a heat sink and Faraday cage (reducing static risk).

Corned Gunpowder

• Process: Dampening the powder and pushing it through a metal sieve to create granules.

• Benefits: All constituents are combined in each granule, improving consistency.

• Still hygroscopic, active to static, and temperature-sensitive BUT everything is together

• Early Cartridges: Wax paper cartridges containing a projectile and propellant were made possible by corned gunpowder.

Modern Smokeless Powder

• Modern ammunition uses cleaner propellants (though some smoke is still produced).

Modern Propellants - Base Compositions

• Distinguished by the number of key compounds: single-base, double-base, and triple-base.

  • Modern cartridges usually use these

Single-Base Propellants

• Common in civilian ammunition.

• Primarily based on nitrocellulose.

• Nitrocellulose:

  • Six times more energetic than corned gunpowder.

  • Created by reacting cellulose with nitric acid.

    • Accidentally discovered when chemist spilled acid on coat

  • Combustion Reaction:

    • C6H8N2O9 + 9O2 \rightarrow 6CO2 + 4H2O + 2N2

    • Products include carbon dioxide, water, and nitrogen gas.

  • Oxygen Deficiency:

    • Nitrocellulose is 35% oxygen deficient, leading to a negative oxygen balance.

    • Lack of oxygen results in the production of carbon monoxide (CO) instead of carbon dioxide (CO_2).

Double-Base Propellants

• Common in military ammunition.

• Consist of nitrocellulose and nitroglycerin.

• Nitroglycerin:

  • Highly shock-sensitive and prone to accidental detonation unless stabilized.

  • More energetic than nitrocellulose.

  • Produces almost no smoke due to efficient combustion.

  • Combustion Reaction:

    • C3H5N3O9 \rightarrow 3CO2 + 5H2O + 3N2 + O2

    • Generates carbon dioxide, water, nitrogen gas, and oxygen.

  • Positive Oxygen Balance:

    • Nitroglycerin produces oxygen, aiding in the combustion of nitrocellulose.

Triple-Base Propellants

• Used in specialist military applications (e.g., rocket propellants).

• Composed of nitrocellulose, nitroglycerin, and nitroguanidine.

• Nitroguanidine:

  • Highly insensitive energetic explosive.

  • Reduces muzzle flash and flame temperature.

  • Reduces barrel erosion.

  • Combustion Reaction:

    • CH4N4O2 \rightarrow CO2 + 2H2O + 2N2

Factors Impacting Weapon and Firearm Health

• Heat: Propellant burning produces heat, which can fatigue the weapon over time due to heating and cooling.

  • Metal bends and flexes easier when hot and if damaged it can lead to a barrel distortion.

  • Cook off: Potential to detonate ammunition in weapon due to heat

  • Can lead to evaporation of lubricants intended to keep firearm in good condition.

Firearm Effectiveness

• Force = Pressure x Area

  • P = F \times A

  • The force applied to the projectile equals the pressure inside the cartridge case multiplied by the cross-sectional area of the bore.

• Fixed Area: Caliber is fixed, so weapon cannot be changed easily

• Adjustable Pressure: The pressure that the propellant generates can be adjusted

• Factors include grain size, grain volume, grain size and packing and chemical additives

• Grain Size & Shape: Decrease grain size to increase surface area and reaction rate.
  * Change shape from disc to perforated disc (donut like) in order to increase surface area

• Smaller Grains: Faster Combustion is needed for smaller handguns in order to generate the optimum pressure.

  • As opposed to bigger weapons where combustion can slowly accumulate due to the bullet spending a longer time inside the barrel.

• Grain Packing Density: Smaller granules have higher interactions between the granules and better heat transferring.

Propellant Grain Examples

• Disc, rod, or lamelle shapes.

• Perforated versions (e.g., perforated disc, tube) increase surface area and reaction rate.

• Toroidal (donut-shaped) and hollow cylinders provide the highest burn rates.

Freshness of Propellants

• Fresh propellant has a sweet smell.

• Old propellant has a bitter and acrid smell.

Additives to Improve Propellant Quality

• Reaction Rate Modifiers: Change burn rates.

  • Examples: dinitrotoluene, carbamate, nitrates.

• Flash Reducers: Reduce muzzle flash.

  • Examples: potassium nitrate, potassium sulfate.

• Wear Reducers: Lower wear on the inside of the barrel.

  • Examples: molybdenum disulfide, titanium dioxide, graphite.

• Stabilizers/Plasticizers: Help in the physical formulation of grains.

  • Examples: resorcinol, diphenylamine, petroleum jelly.

• De-Coppering Agents: Reduce copper deposition.

  • Examples: tin, bismuth, tin dioxide.

• Summary: There are many elements that affect combustion and therefore also affect pressure. In order to be safe and effective these need to understood.

Housekeeping Notices

• Labs Continuing: Ballistics labs continue this week, focusing on advanced trajectory analysis and terminal ballistics. Ensure you have your safety gear and data recording equipment ready. Prepare by reviewing the lab scripts, understanding the tasks, and familiarizing yourself with the data analysis software.

• Lab Write-Ups: If you attended labs last week, ensure your write-ups are completed or in progress. Pay attention to detail and clearly articulate your methodologies, results, and conclusions. Submit your reports promptly to receive timely feedback.

• Presentations on Thursday: Finalize group preparations for presentations this Thursday. Coordination is key, and each member should know their role and material thoroughly. If there are any issues within the group, address them promptly and respond to the email sent out by the instructor.

  • Seek guidance from the instructor or TA if needed.

• Slide Upload: Upload presentation slides 24 hours before your presentation slot. This is needed to ensure a smooth transition between groups and allows time for technical checks. Use a standard presentation format (e.g., PowerPoint or PDF) to avoid compatibility issues.

• Jury Duty: Last two court sessions this year on Wednesday afternoon/evening and Thursday late afternoon/early evening. These sessions will cover complex forensic evidence. Attend if you still need to fulfill your duty or want additional experience in legal proceedings.

Primers and Propellants

• Difference between Primers and Propellants:

  • Primers: Detonate (explode) at supersonic speeds, initiating the propellant combustion. The rapid expansion creates the initial shockwave.

  • Propellants: Burn at subsonic speeds (deflagration). Designed to produce a sustained pressure to propel the projectile.

• Deflagration: A subsonic combustion event propagating through thermal conductivity, where each layer heats the next. This controlled burn is essential for safe and effective propulsion.

• Propellants are designed to deflagrate, not detonate, within the ammunition system to prevent catastrophic failure.

• Propellants can explode under specific conditions (e.g., high containment, extreme temperatures, or improper handling).

Types of Propellants

• Historic vs. Modern Propellants: Older systems still work and are relevant in understanding potential criminal uses of firearms. Understanding these propellants can aid in forensic analysis.

Black Powder

• History: Dates back to before 424 BC, used in pyrotechnics by the Chinese for generating gas to launch projectiles (e.g., rockets and fireworks).

• Usage: Historically used in muzzle-loading firearms, cannons, and early explosive devices.

• Modern Usage: Still used in older fire arm reenactments, historical demonstrations, and some niche modern applications.

• Composition:

  • 14\%\text{ Sulphur}

  • 10\%\text{ Carbon}

  • 76\%\text{ Potassium Nitrate}

• Potassium Nitrate: Acts as the oxidizer and fuel, driving the explosive reaction; also known as saltpeter and used in fertilizers. It provides the oxygen needed for combustion.

• ANFO (Ammonium Nitrate Fuel Oil): An explosive composition that can sometimes use potassium nitrate instead of ammonium nitrate, commonly used in industrial blasting.

• Black Powder Reaction: 4KNO3(s) + 7C(s) + S(s) \rightarrow 3CO2(g) + N2(g) + K2S(s) + K2CO3(s)

  • Products include carbon dioxide, nitrogen gas, and potassium sulfide (a solid residue). The rapid production of gas creates pressure.

• Potassium Sulfide:

  • Can cause fouling (residue buildup) in gun barrels. This fouling affects accuracy and can damage the firearm.

  • Reacts with water to form sulfuric acid, leading to weapon erosion and corrosion. Proper cleaning is crucial.

• Mixture Challenges:

  • If not ground to the same particle size, components separate easily due to density differences, leading to inconsistent performance.

  • Milling is a process of grinding constituents to ensure consistent mixture and performance, improving combustion efficiency and reliability.

• Ineffective Combustion:

  • Produces partially burned residues and significant smoke (large plumes). This reduces efficiency and increases visibility.

  • Smoke reveals the shooter's position and obstructs their view, making it tactically disadvantageous.

• Fouling:

  • Residues that build up inside the barrel, potentially blocking bullet transit. This can cause misfires or damage the firearm.

  • Regular weapon maintenance is essential to prevent fouling and ensure reliable operation.

• Disadvantages:

  • Hygroscopic: Absorbs moisture from the air, leading to toxic byproducts (sulfuric acid). This degrades the powder and corrodes the firearm.

  • Unstable when hot: Has a low cook-off temperature, increasing the risk of accidental ignition.

  • Highly sensitive to static electricity, requiring careful handling to prevent accidental ignition.

• Modern Improvements:

  • Enclosed brass cartridge systems prevent water ingress, protecting the powder from moisture.

  • Brass acts as a heat sink and Faraday cage (reducing static risk), enhancing safety and reliability.

Corned Gunpowder

• Process: Dampening the powder and pushing it through a metal sieve to create granules. This process improves handling and consistency.

• Benefits: All constituents are combined in each granule, improving consistency and leading to more uniform combustion.

• Still hygroscopic, active to static, and temperature-sensitive, BUT everything is together, making it easier to handle and more reliable than loose black powder.

• Early Cartridges: Wax paper cartridges containing a projectile and propellant were made possible by corned gunpowder, simplifying loading and improving portability.

Modern Smokeless Powder

• Modern ammunition uses cleaner propellants (though some smoke is still produced). These propellants offer higher energy and reduced residue.

Modern Propellants - Base Compositions

• Distinguished by the number of key compounds: single-base, double-base, and triple-base. These determine the propellant's energy, burning characteristics, and application.

• Modern cartridges usually use these due to their improved performance and safety characteristics.

Single-Base Propellants

• Common in civilian ammunition for its balance of performance and cost.

• Primarily based on nitrocellulose.

• Nitrocellulose:

  • Six times more energetic than corned gunpowder, providing higher velocities and flatter trajectories.

  • Created by reacting cellulose with nitric acid, a process that nitrates the cellulose and makes it highly flammable.

  • Accidentally discovered when a chemist spilled acid on a coat, leading to the development of modern propellants.

  • Combustion Reaction: C6H8N2O9 + 9O2 \rightarrow 6CO2 + 4H2O + 2N2

  • Products include carbon dioxide, water, and nitrogen gas. The rapid formation of these gases generates pressure.

  • Oxygen Deficiency: Nitrocellulose is 35% oxygen deficient, leading to a negative oxygen balance.

  • Lack of oxygen results in the production of carbon monoxide (CO) instead of carbon dioxide (CO_2), which reduces energy efficiency.

Double-Base Propellants

• Common in military ammunition, offering higher energy and performance under extreme conditions.

• Consist of nitrocellulose and nitroglycerin.

• Nitroglycerin:

  • Highly shock-sensitive and prone to accidental detonation unless stabilized. Desensitizers are added to improve safety.

  • More energetic than nitrocellulose, providing increased power and velocity.

  • Produces almost no smoke due to efficient combustion, making it ideal for tactical applications.

  • Combustion Reaction: C3H5N3O9 \rightarrow 3CO2 + 5H2O + 3N2 + O2

  • Generates carbon dioxide, water, nitrogen gas, and oxygen. The release of oxygen further enhances combustion.

  • Positive Oxygen Balance: Nitroglycerin produces oxygen, aiding in the combustion of nitrocellulose and improving overall efficiency.

Triple-Base Propellants

• Used in specialist military applications (e.g., rocket propellants and large-caliber ammunition), providing tailored performance characteristics.

• Composed of nitrocellulose, nitroglycerin, and nitroguanidine.

• Nitroguanidine:

  • Highly insensitive energetic explosive, improving safety during handling and storage.

  • Reduces muzzle flash and flame temperature, minimizing visibility and reducing the risk of detection.

  • Reduces barrel erosion by lowering combustion temperatures and minimizing corrosive byproducts.

  • Combustion Reaction: CH4N4O2 \rightarrow CO2 + 2H2O + 2N2

Factors Impacting Weapon and Firearm Health

• Heat: Propellant burning produces heat, which can fatigue the weapon over time due to heating and cooling cycles. This thermal stress affects the metal's mechanical properties.

  • Metal bends and flexes easier when hot, and if damaged, it can lead to a barrel distortion. This affects accuracy and can cause dangerous malfunctions.

  • Cook off: Potential to detonate ammunition in weapon due to heat. This is a critical safety concern, especially in automatic weapons.

  • Can lead to evaporation of lubricants intended to keep firearm in good condition, increasing friction and wear.

Firearm Effectiveness

• Force = Pressure x Area

  • F = P \times A

  • The force applied to the projectile equals the pressure inside the cartridge case multiplied by the cross-sectional area of the bore. This relationship governs the projectile's acceleration and velocity.

• Fixed Area: Caliber is fixed, so weapon cannot be changed easily. This limits the potential for increasing force through altering the bore diameter.

• Adjustable Pressure: The pressure that the propellant generates can be adjusted by modifying propellant characteristics.

• Factors include grain size, grain volume, grain shape and packing, and chemical additives.

• Grain Size & Shape: Decrease grain size to increase surface area and reaction rate. This allows for faster pressure buildup.

  • Change shape from disc to perforated disc (donut like) in order to increase surface area and control the burn rate.

• Smaller Grains: Faster Combustion is needed for smaller handguns in order to generate the optimum pressure quickly.

  • As opposed to bigger weapons where combustion can slowly accumulate due to the bullet spending a longer time inside the barrel. This allows for a more sustained pressure.

• Grain Packing Density: Smaller granules have higher interactions between the granules and better heat transferring, leading to more uniform combustion.

Propellant Grain Examples

• Disc, rod, or lamelle shapes, each designed to produce specific burning characteristics.

• Perforated versions (e.g., perforated disc, tube) increase surface area and reaction rate, allowing for more controlled and rapid combustion.

• Toroidal (donut-shaped) and hollow cylinders provide the highest burn rates, suitable for specialized applications requiring rapid pressure generation.

Freshness of Propellants

• Fresh propellant has a sweet smell, indicating proper storage and minimal degradation.

• Old propellant has a bitter and acrid smell, signaling decomposition and potential instability.

Additives to Improve Propellant Quality

• Reaction Rate Modifiers: Change burn rates, allowing for tailored performance characteristics.

  • Examples: dinitrotoluene, carbamate, nitrates. These compounds either accelerate or decelerate the combustion process.

• Flash Reducers: Reduce muzzle flash, minimizing visibility and reducing the risk of detection.

  • Examples: potassium nitrate, potassium sulfate. These suppress the secondary combustion of gases.

• Wear Reducers: Lower wear on the inside of the barrel, extending the firearm's lifespan.

  • Examples: molybdenum disulfide, titanium dioxide, graphite. These act as solid lubricants, reducing friction.

• Stabilizers/Plasticizers: Help in the physical formulation of grains, ensuring consistent and reliable combustion.

  • Examples: resorcinol, diphenylamine, petroleum jelly. These maintain the propellant's physical integrity.

• De-Coppering Agents: Reduce copper deposition in the barrel, maintaining accuracy and reducing cleaning frequency.

  • Examples: tin, bismuth, tin dioxide. These react with copper residues, preventing buildup.

• Summary: There are many elements that affect combustion and therefore also affect pressure. In order to be safe and effective these need to understood. Proper understanding ensures safety, effectiveness, and consistency in firearm performance.