LO5 Ballistics Flashcards
What is ballistics?
The scientific study of the motion of projectiles
What’s happening inside the chamber?
- Since the projectile isn’t moving, the volume in the chamber is constant.
- The temperature and pressure are increasing, causing the burn rate to increase.
High pressures and temperatures will increase the burn rate - The propellant’s performance characteristics will dictate how long this phase will last.
The pressure required to force the projectile to move is known as the shot start pressure. - The pressure must be sufficient to force the engraving band into the lands of the rifling.
- The Burning Rate of the propellant will have an effect of when the shot start pressure will be reached.
Burning characteristics
- Propellant Composition
Burning Rate
Pressure Index
Force Constant
Co Volume - Propellant Granule
The Ballistic Size
The Form Function
Burning characteristics explanation
- Propellant Composition
Burning Rate - Is the rate at which a granule reduces in size as the burning of that granule occurs on all sides
Pressure Index - Coefficient which relates to changes in burning rate to changes in pressure
Force Constant - A measure of the pressure which a unit mass of propellant produces in a fixed volume
Co Volume - The volume occupied by the molecules of a kilogram of propellant in a gaseous state - Propellant Granule
The Ballistic Size - Is the shortest distance between any two points on the surface of a propellant granule
The Form Function - How the surface area of a propellant grain of a particular shape changes during combustion.
Objectives of Internal Ballistics
- Launch the Projectile safely
- Consistent performance between shots
- Achieve the highest possible muzzle velocity
Phases of internal ballistics
- Charge Ignition
- Combustion prior to projectile motion
- Combustion up to the all burnt point
- Gas flow and Projectile motion after all burnt point to muzzle
Percentages of distribution of energy during firing sequence
- Projectile (translational & rotational) = 32%
- Residual heat of the gases = 42%
- Recoil of the gun = 0.2%
- Engraving the driving band/barrel friction = 2.8%
- Unburnt charges and gases = 3%
- Heat lost to the gun = 20%
Ballistic Abnormalities
- Occasion-to-occasion Effect
- The Warmer (Cold Gun) Effect
- Order of Fire
- Ballistic Hump
Define Internal ballistics
The scientific study of the operating process within the gun from the moment that the propellant is ignited until the projectile leaves the barrel
Define Pioberts Law
The surface of a Burning propellant recedes layer by layer in a direction normal to the surface.
Propellant form functions
**Granual Shape Approx Form Function
Random Chip Positive Most Degressive
Spherical Positive
Cylindrical Cord Positive
Disc Positive Near Zero
Tube/SlottedTube Positive Near Zero Neutral
Ribbon Positive Near Zero
Solid (Suppressed outer layers) Near Zero
Multi tube Near Zero
Tube (Inhibited Ign of outer surface) Negative Most Progressive
What happens to the rate of burning of propellant if the pressure is increased?
It increases.
How can the round to round regularity of muzzle velocity be improved?
If burning finishes while the shell is still well back in the bore.
What is the effect of an increase in charge weight?
Pressure increases, ABP moves back, muzzle velocity increases, regularity in fall of shot improves.
For the same weight of charge, what is the effect of increasing the propellant size?
Total initial burning surface of the propellant decreases.
Pressure is lower at first, ABP moves forward in the bore, muzzle velocity decreases, regularity in fall of shot decreases.
What is the effect of using a multi tubular propellant on internal ballistics?
The peak pressure is reduced but the projectile still gets good energy levels.
What is the effect on internal ballistics of using a projectile of normal weight, but shorter and of larger diameter than normal?
The same muzzle velocity is achieved with a pressure which is everywhere less than with the standard shot.
