Lecture 7 - Internal Ballistics

Internal ballistics: Study of firearm processes from trigger pull to projectile exit.

Dynamics: Encompasses pressure, velocity, energy transfer, and thermochemical processes.

Importance: Optimizes design, ensures safety, and assesses performance.

Key Stages:

• Lock time: Firing mechanism initiation to primer ignition.

• Ignition time: Primer ignition to projectile movement.

• Barrel time: Projectile travel through the barrel.

• Understanding: Holistic view for effective analysis.

Chamber Pressures: Can exceed 3500 atmospheres (51,450 PSI).

Projectile Velocities: Can surpass 1000 m/s in 0.02 seconds.

Safety: Demands robust materials and engineering.

Ballistic Efficiency: Ratio of projectile KE to propellant chemical energy.

• Factors: Propellant type, barrel length, projectile-barrel fit.

Lock Time:

• Definition: Interval between firing activation and primer ignition.

• Shorter Time: Minimizes shooter movement influence, improves accuracy.

• Influence: Trigger mechanism design, mechanical properties.

• Mechanical Systems: Sears favored for reliability; critical sear design.

• Safety: Mechanisms prevent unintended discharges.

Firearm Safety Mechanisms:

• Trigger Safety: Blocks trigger movement; may not prevent sear failure discharge.

• Sear Safety: Blocks trigger sears; failure possible if tampered.

• Grip Safety: Requires grip compression; found in SLPs and SMGs.

• Fire Selection Lever: Controls firing mode; blocks sear engagement in 'safe'.

• Magazine Interlock: Prevents discharge without magazine; tactical disadvantage.

• Firing Pin Safety: Blocks firing pin movement with spring-loaded plunger.

Accidental Firearm Discharge:

• Investigations: Requires mechanical examination, ensuring safety.

• Safety Failure Test: Reveals safety failures with dry-firing and impact tests.

• Trigger Test: Measures trigger pull; deviations indicate tampering.

• Pull Pressures: Vary by firearm (15-25 N for .22 rifles, 20-35 N for assault rifles).

Ignition Time:

• Definition: Duration from primer activation to projectile movement.

• Dependence: Primer type, propellant design, chamber dimensions, bullet crimping.

• Firing Sequence: Firing pin crushes primer, igniting mixture, creating hot gases.

• Propellants: Deflagrate at controlled rates; tailored composition.

Barrel Time:

• Definition: Interval from projectile movement to muzzle exit.

• Influence: Projectile, friction, rifling, pressure, burn rate.

• Projectile Motion: Undergoes acceleration based on forces and distance.

Pressure Equations:

• Ideal Gas Law: $P = \frac{nRT}{V}$$$P = \frac{nRT}{V}$$

• Boyle’s Law: $P1V1 = P2V2$$$P1V1 = P2V2$$

• Description: Ideal Gas Law relates pressure, volume, temperature, and moles; Boyle’s Law relates pressure and volume.

Projectile Forces:

• Motion: Experiences acceleration and rotational forces.

• Calculations: $F=ma$$$F=ma$$, kinematic equations.

Air Weapons:

• Spring Operated:

• Phases: Lock, compression, and barrel time.

• Mechanism: Trigger releases spring; piston compresses air.

• Pre-Charged Pneumatic (PCP):

• Phases: Lock, valve operation, and barrel time.

• Mechanism: Valve system meters compressed air.

• Energy Regulations (UK):

• Licensing: <12 ft-lb muzzle energy: no license; >12 ft-lb: certifications.

The Home Office Test for Air Weapons:

• Measurement: Determines muzzle energy with varied pellet weights.

• Muzzle Energy Equation: $Ek=\frac{1}{2}mv^2$$$Ek=\frac{1}{2}mv^2$$

• Legal Classification: Exceeding limits classifies as a firearm.

Handloading:

• Definition: Manual reloading of cartridges.

• Risks:

• Excessive Pressure: Can cause firearm failure.

• Insufficient Pressure: Can lodge bullet, causing explosion.