Behavior of interior ballistics

Answer 1

Interior ballistics refers to the processes and phenomena that occur within the chamber of a firearm or artillery piece from the time of ignition of the propellant until the projectile exits the barrel. Understanding interior ballistics is crucial for the design and performance optimization of firearms and ammunition. Here are the key phases and behaviors:

1. **Ignition Phase**: This is the initial stage where the primer ignites the propellant. The primer's explosion creates a small but intense flame that rapidly ignites the propellant near the primer.

2. **Burning Phase**: Once ignited, the propellant starts to burn, converting chemical energy into heat and expanding gases. The nature of the propellant burn can vary:
- **Progressive Burn**: The burn rate increases over time, typically achieved with slow-burning powders that have large surface areas.
- **Degressive Burn**: The burn rate decreases over time, usually characteristic of fast-burning powders with small surface areas.
- **Neutral Burn**: A constant burn rate is maintained, often associated with propellants having a consistent surface area during burning, like cylindrical grains with central perforations.

3. **Pressure Build-Up**: As the propellant burns, gases are produced, increasing the pressure within the chamber. The rate of pressure build-up depends on the burn characteristics of the propellant and the confinement of the chamber.

4. **Projectile Movement**: Under the rapidly increasing pressure, the projectile starts moving down the barrel. Initially, there's a resistance to overcome (shot start pressure), and once this is surpassed, the projectile accelerates.

5. **Barrel Dynamics**: As the projectile moves, it experiences friction against the barrel's walls and rifling, which imparts a rotational spin for stability. The interaction between the projectile and barrel rifling affects the interior ballistics.

6. **Pressure and Velocity Curve**: The internal pressure typically peaks shortly after ignition and then gradually drops as the projectile travels down the barrel, resulting in a specific pressure-time curve. The velocity of the projectile increases as it moves, dictated by the pressure behind it and the barrel length.

7. **Burn Out**: Ideally, by the time the projectile reaches the barrel's end, the propellant should be fully combusted, using up its chemical energy efficiently. In some cases, partial burning can continue post-barrel exit, which is less efficient and can affect accuracy.

8. **Heat Effects**: The combustion process generates significant heat within the chamber and barrel. This heat can affect subsequent rounds, influencing the performance consistency due to temperature variations.

9. **Residual Effects**: After the projectile exits, residues of propellant and gases remain, contributing to fouling and affecting the firearm's performance over time. Proper cleaning and maintenance are essential.

Understanding these phases helps in designing better firearms and ammunition by considering factors like propellant type, projectile design, chamber and barrel materials, and other engineering aspects to achieve optimal performance, safety, and longevity.