Lecture 9 - Primers and Propellants (skim)

Primers

• Two main designs of centre-fire primers:

  • Boxer: Features a central anvil within the primer cup and a single flash hole in the cartridge case. Easier to reload due to the single point of ignition.

  • Berdan: Uses an anvil that is an integral part of the cartridge case with multiple flash holes.

• Typical primer charge: Lead Styphnate C6HN3O*8Pb - Primary high explosive, detonated by friction, impact, or flame.

  • Detonation velocity: 5200 ms^{-1}

Rim-fire Cartridges

• Firing pin impacts the rim of the cartridge case.

• Cheaper to make, suitable for lower energy rounds (0.22" or 5.5 mm caliber).

Propellants

• Energetic materials that deflagrate (subsonic combustion) to propel projectiles.

• Black powder:

  • 14% Sulphur (S): Acts as a stabilizer and fuel.

  • 10% Carbon (C): Provides fuel for the reaction.

  • 76% Potassium Nitrate (KNO3): Oxidizer that supports combustion.

  • 2KNO3(s) + 3C(s) + S(s) \rightarrow 3CO2(g) + N2(g) + K2S(s)

• Corned gunpowder: Dampened black powder mixture pressed through a metal screen. This process creates grains of more consistent size, improving burn consistency.

Modern Propellants

• Single base: Nitrocellulose (NC). Provides the main energetic component.

• Double base: Nitrocellulose (NC) and Nitroglycerine (NG). Increases energy and propellant density.

• Triple base: Nitrocellulose (NC), Nitroglycerine (NG) and Nitroguanidine (NGu). Used in large caliber guns to reduce muzzle flash and erosion.

Energetic Material

• Nitrocellulose (NC):

  • 4C6H7N3O{11} + 9O_2 \rightarrow

  • 35% O_2 deficient: Requires additional oxidizers for complete combustion.

• Nitroglycerine (NG):

  • 4 C3H5(ONO2)3 \rightarrow

  • Positive oxygen balance: Burns more completely, increasing energy output.

• Nitroguanidine (NGu):

  • H4N4CO2 \rightarrow 2 H2O + 2 N_2 + C

  • Reduces muzzle flash and flame temperature: By absorbing heat and producing cooling gases.

Heat Effects

• Heat build-up:

  • Barrel distortion: High temperatures can cause the barrel to warp, affecting accuracy.

  • Cook off: Cartridge self-ignites due to excessive heat.

  • Evaporation of lubricants: Reduces the effectiveness of lubrication, increasing wear.

Firearm System Effectiveness

• F = P \times A

  • F: Force applied to the projectile

  • P: Peak chamber pressure

  • A: Bore cross-sectional area

Propellant Properties

Maintaining optimal chamber pressure is essential.

• Grain size and shape: Affects burn rate. Smaller grains burn faster, increasing pressure rapidly; larger grains burn slower, providing more sustained pressure.

• Chemical additives

  • Reaction rate modifiers: Control the speed at which the propellant burns.

  • Flash reducers: Compounds added to propellants to decrease the amount of visible light produced during firing.

  • Wear reducers: Materials added to reduce friction and wear on the gun barrel.

  • Stabilisers and plasticisers: Stabilisers prevent the propellant from degrading

Primers

• Two main designs of centre-fire primers:

  • Boxer: Features a central anvil within the primer cup and a single flash hole in the cartridge case. Easier to reload due to the single point of ignition.

  • Berdan: Uses an anvil that is an integral part of the cartridge case with multiple flash holes.

• Typical primer charge: Lead Styphnate C6HN3O*8Pb - Primary high explosive, detonated by friction, impact, or flame.

  • Detonation velocity: 5200 ms^{-1}

Rim-fire Cartridges

• Firing pin impacts the rim of the cartridge case.

• Cheaper to make, suitable for lower energy rounds (0.22" or 5.5 mm caliber).

Propellants

• Energetic materials that deflagrate (subsonic combustion) to propel projectiles.

• Black powder:

  • 14% Sulphur (S): Acts as a stabilizer and fuel.

  • 10% Carbon (C): Provides fuel for the reaction.

  • 76% Potassium Nitrate (KNO3): Oxidizer that supports combustion.

  • 2KNO3(s) + 3C(s) + S(s) \rightarrow 3CO2(g) + N2(g) + K2S(s)

• Corned gunpowder: Dampened black powder mixture pressed through a metal screen. This process creates grains of more consistent size, improving burn consistency.

Modern Propellants

• Single base: Nitrocellulose (NC). Provides the main energetic component.

• Double base: Nitrocellulose (NC) and Nitroglycerine (NG). Increases energy and propellant density.

• Triple base: Nitrocellulose (NC), Nitroglycerine (NG) and Nitroguanidine (NGu). Used in large caliber guns to reduce muzzle flash and erosion.

Energetic Material

• Nitrocellulose (NC):

  • 4C6H7N3O{11} + 9O_2 \rightarrow

  • 35% O_2 deficient: Requires additional oxidizers for complete combustion.

• Nitroglycerine (NG):

  • 4 C3H5(ONO2)3 \rightarrow

  • Positive oxygen balance: Burns more completely, increasing energy output.

• Nitroguanidine (NGu):

  • H4N4CO2 \rightarrow 2 H2O + 2 N_2 + C

  • Reduces muzzle flash and flame temperature: By absorbing heat and producing cooling gases.

Heat Effects

• Heat build-up:

  • Barrel distortion: High temperatures can cause the barrel to warp, affecting accuracy.

  • Cook off: Cartridge self-ignites due to excessive heat.

  • Evaporation of lubricants: Reduces the effectiveness of lubrication, increasing wear.

Firearm System Effectiveness

• F = P \times A

  • F: Force applied to the projectile

  • P: Peak chamber pressure

  • A: Bore cross-sectional area

Propellant Properties

Maintaining optimal chamber pressure is essential.

• Grain size and shape: Affects burn rate. Smaller grains burn faster, increasing pressure rapidly; larger grains burn slower, providing more sustained pressure.

• Chemical additives

  • Reaction rate modifiers: Control the speed at which the propellant burns.

  • Flash reducers: Compounds added to propellants to decrease the amount of visible light produced during firing.

  • Wear reducers: Materials added to reduce friction and wear on the gun barrel.

  • Stabilisers and plasticisers: Stabilisers prevent the propellant from degrading