INTERNAL BALLISTICS OF SMALL ARMS

 

Internal Ballistics in Small Arms

Internal Ballistics deals with the processes that occur inside a firearm from the moment the trigger is pulled until the bullet exits the barrel. Understanding these processes is crucial for optimizing firearm performance, ensuring safety, and improving the precision and reliability of the weapon. Below is a detailed exploration of the various factors and phenomena involved in internal ballistics.

A.    Ignition:

·        Trigger Action: When the trigger is pulled, the firing pin strikes the primer of the cartridge, igniting the primer compound.

·        Primer Reaction: The primer generates a small, controlled explosion, producing the hot gases that ignite the propellent (gunpowder) with in the cartridge.

·        Timing: The speed of the ignition is crucial for consistent performance. A delay in ignition can affect accuracy and shot consistency.

 

B.     Burning of Propellants:

·        Progressive Burning: Modern gunpowder is designed to burn progressively, meaning the surface area exposed to combustion increases as the powder burns, maintaining high pressure within the chamber.

·        Rate of Burn: The burn rate is influenced by the chemical composition of the propellent and its granule size. A faster burn rate generally generates higher pressure more quickly, while slower burning powders produce more sustained pressure.

·        Degressive Powder: It is a type of gunpowder that burns quickly at first, creating a lot of pressure, but then slows down as it burns. This type of powder is useful in ammunition where you need a strong initial push for the bullet but do not want too much pressure after that, like in guns with shooter barrels or for certain types of small bullets.

Mostly it comes in shape like flakes or discs. These shapes have a large surface area initially, which decreases as the powder burns, leading to a degressive burn pattern.

·        Progressive Powder: This type of gunpowder burns more and more as it goes, increasing pressure to keep pushing the bullet with more force. It is good for longer barrels, where the bullet needs a strong and steady push.

Burn rate of progressive powder is starts slower and gradually speed up, creating more gas and pressure as the bullet moves down the barrel. And the pressure increases progressively, which helps push the bullet through the barrel with sustained force. It comes in cylindrical and spherical grains.

 

C.    Geometry of Gunpowder:

·        Shape of Granules: Gun powder can come in different shapes, such as spherical, flake, or cylindrical. Each shape affects how the powder burns, with extruded powders often burning more progressively than spherical powders.

·        Surface Area: The shape and size of the granules determine the total surface area available for combustion, which directly influences the burn rate and the pressure curve inside the barrel.

 

D.    Pressure and Its Measurement:

·        Chamber Pressure: This is the pressure generated with in the cartridge chamber due to the burning propellent. High chamber pressure propels the bullet through the barrel.

·        Measurement: Pressure is typically measures in pounds per square inch (PSI) using piezoelectric transducers or copper crushers. Understanding pressure dynamics is critical to avoid overpressure situations, which can cause barrel rupture or excessive recoil.

 

E.     Lock Time:

·        Definition: Lock time is the interval between pulling the trigger and the firing pin striking the primer. Shorter lock time contribute to better accuracy, as there is less time for the shooter to inadvertently move the weapon before the shot is fired.

 

F.     Ignition Time:

·        Definition: This is the time between the firing pin striking the primer and the full ignition of the propellent. Variability in ignition time can affect shot consistency and accuracy.

·        Influencing Factors: Primarily influenced by the types of primer, sensitivity of the primer, quality of the primer and the design of the cartridge.

G.    Barrel Time:

·        Definition: Barrel time refers to the duration from the moment the bullet starts moving until it exists the barrel. It is a critical factor in shot placement, as external forces such as the shooters movement can impact the bullet during this time.

 

H.    Atmospheric Conditions:

·        Temperature and Humidity: These can affect the pressure and burn rate of the propellent. Higher temperatures typically increase the burn rate, while higher humidity can lead to inconsistent performance due to moisture absorption by the propellent. Also, in hot places the firearm may burst when the pressure developed at an excessive rate. In cold places, the ammunition may develop low velocities. There is variation in velocities because of temperature is about one meter per second.

·        Air Pressure: Changes in atmospheric pressure can also influence the bullets behavior as it exits the barrel, but this falls more into external ballistics.

 

I.      Shape of Cartridges:

·        Case Design: The shape and dimensions of the cartridge case influence how the propellent burns and the efficiency of gas sealing with in the chamber.

·        Bottleneck vs Straight walled: Bottle neck cases often allow for higher pressures and velocities, whereas straight walled cases may produce lower pressures but offer more reliable feeding in some firearms.

 

J.      Density of Loading:

·        Loading Density: This is the ratio of the volume of the powder charge to the volume of the cartridge case. High loading density typically results in more consistent burn rates and pressure curves.

 

The density of loading and combustion rate,

S = U/V * 100

Were,

U – is the volume that is occupied by the powder

V – is the volume of the cartridges case

S – is the density of loading.

In the rifle’s Cartridge, the loading density varies from 75 to 95. Higher densities are more useful. Because they permit uniform burning, proper development of pressure, economical, and give rise to regular velocities. Low loading densities may result in giving hand fire, some times improper loading density material affect the range and aim of a shot.

·        Over or Under loading: An underloaded cartridge can cause erratic combustion, leading to dangerous pressure spikes, while overloading can exceed the design limits of the firearm, leading to catastrophic failures.

 

K.    Heat Problems and Combustion of Propellants:

During the combustion of propellants, the temperature is often taught to 3000 degrees Celsius. Some times a barrel of a firearm melts at these temperatures if gases at this temperature remain in the barrel for a long time. But fortunately, the time for which the hot gases are in contact with the barrel is about 0.001 seconds.

 

L.     Pressure Curve:

·        Chamber Pressure: Chamber pressure is the pressure exerted by a cartridge case outside walls onto the inside of a firearms chamber when the cartridge is fired. It is generally expressed in pounds per square inch or copper units of pressure.

 

Pressure development inside the barrel depends upon certain characteristics which are given below;

 

(a)    Quantity or quality of powder charge

(b)   Available space for expansion

(c)    Speed of initiation and burning

(d)   Chemical nature of the powder

(e)    Surface area

(f)    Pressure determination

The pressure developed by ammunition is always measured to find out if the same is within the safe limits or not. Generally, this is done in the ordinance factory.

The formula for pressure determination:

P = KW

W – is the weight of powder in grains

K – is the constant value

There are three methods generally used to determine the pressures.

(a)    Crusher technique

(b)   Piezo technique

(c)    Strain gauge method

 

M Twist of Rifling:

·        Rifling: The grooves inside the barrel that impart a spin to the bullet. The rate of twist, measured in inches per turn.

·        Impact on Velocity: A faster twist rate can stabilize longer, heavier bullets but may increase friction and reduce velocity slightly. Conversely, a slower twist rate may be insufficient to stabilize the bullet, affecting accuracy.

 

N.    Bullet Fit and Velocity of Bullet:

·        Bullet Fit: The bullet must fit snugly in the barrel to create a proper gas seal, preventing gas from escaping around the bullet (known as blow by). Proper fit is crucial for accuracy and consistent velocity.

·        Muzzle Velocity: The speed of the bullet as it exists the barrel is a key performance metric, influenced by barrel length, propellent type, and bullet weight. Higher velocities generally improve range and penetration but can increase barrel wear.

 

O.    Strength of Barrel:

·        Material and Design: Barrel strength is determined by the materials used such as steel, etc. and the thickness of the barrel walls. The barrel must withstand the high pressure generated during firing without deforming or rupturing.

·        Stress Handling: Proper heat treatment and material selection are critical to ensure the barrel can endure repeated firing without succumbing the fatigue or failure.

 

P.     Erosion:

·        Bore Erosion: Over time, the hot gases and friction from the bullet can erode the barrel, particularly near the chamber. Erosion reduces accuracy and can eventually lead to barrel failure.

·        Mitigation: Chrome lining, nitriding, and other surface treatments can slow erosion and extend barrel life.

 

Q.    Corrosion or Rusting of Barrel:

·        Causes: Exposure to moisture, salts, environmental exposure and residue from corrosive primers can cause rust and corrosion, weakening the barrel.

·        Prevention: Regular cleaning, use of protective coatings, and proper storage can prevent corrosion.

 

R.    Bullet of the Weapon:

·        Design and Material: Bullets are typically made from lead, jacketed in copper or another metal. Bullet shape such as hollow point, full metal jacket affects the terminal ballistics but also impacts in internal ballistics through friction and gas sealing.

·        Weight: Heavier bullets generate more recoil and typically have lower velocities, but they can offer better penetration and energy retention.

 

S.     Recoil of the Weapon:

·        Newtons Third Law: For every action, there is an equal and opposite reaction. The force propelling the bullet forward generates a rearward force, known as recoil.

·        Impact on Accuracy:  Recoil affects the shooters’ ability to maintain a steady aim, particularly in rapid fire scenarios. Reducing recoil through mechanisms like muzzle brakes, recoil pads, or using lighter bullets can improve accuracy and comfort, some times it injures the shooter if the weapon is not held properly or recoil velocity is excessive.

For reducing recoil, the compensators are used. It helps in eliminating recoil due to blast, sometimes muzzle velocity of projectile and gases.

 

T.     The Phenomenon of Bursting Barrel:

·        Overpressure: A barrel can burst if the pressure inside exceeds its design limits. This can be caused by overloading, barrel obstructions (e.g., debris, a stuck bullet), or material defects.

·        Prevention: Proper maintenance, adherence to loading specifications, and regular inspection for wear and defects are crucial to preventing barrel bursts.