Internal Ballistics:
Internal ballistics is the study, which deals with the motion of projectile(s) in the bore of the weapon whereas external ballistics deals with the flight from the muzzle of the weapon to the target.
It commences as soon as the first grain of propellant is ignited and Proceeds till the Projectile leaves the muzzle of the weapon.
The study includes all the details concerning the impulse which makes the projectile move out from the muzzle in the air.
As a matter of fact, the projectile obtain its energy during the period it remains in the firearms.
This period can be divided as follows:
1.Lock Time:
The lock time is the period of time between the release of the sear and the striker's collision with the percussion cap. Rapid fire is more favourable with a short internal time. There are several techniques to measure the lock time, and one such system makes use of linear motion sensors and an oscilloscope.
2.Ignition time:
The ignition time is the amount of time that passes between the firing pin being struck and the first grain of powder blowing up. In typical circumstances, the ignition takes place at an interval of about 0.002 seconds.
3.Barrel Time:
The amount of time between pulling the trigger and the bullet leaving the muzzle end is known as the barrel time.
In case of most of the weapons Lock time + Ignition time + barrel time varies from 0.003 to 0.007 seconds.
Phenomenon of Internal ballistics:
1.Ignition:
When the firing pin strikes the hammer, the priming compound explodes quickly, creating a jet of flames with a very high temperature that enters the propellant chamber through the flash hole. The propellant, which burns quickly to produce a large volume of high pressure gas and accelerate the bullet down the barrel and out the muzzle end, is ignited by this jet of flame, which has a temperature of roughly 2000°C.
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2.Burning of Propellant:
Nitrocellulose propellants will burn gently if lit in an open area. If it is in a confined location, the heat and pressure created will exponentially increase the rate of burning.
The products of combustion in case of Nitroglycerine are as detailed below:
Nitroglycerine+Carbon dioxide + water Vapours + Oxides of Nitrogen + Nitrogen + Heat
At normal Temperature (0 °C) and Pressure (760 mm), 1 gm of Nitroglycerin will 1000 Cubic centimetres of Gases. The process produces a lot of heat, roughly a thousand calories worth. The temperature may rise beyond 3000 °C. Just a part of this energy is transformed into the projectile's kinetic energy. It is largely squandered.
When used as a weapon, the propellant is contained in a cartridge case with a bullet sealing the mouth. The chamber walls and standing breech of the weapon then sustain the round of ammunition. Under these circumstances, the pressure buildup will continue until it is high enough to overcome the bullet's inertia and cause it to begin accelerating down the bore. The pressure and resistance increase as the bullet weight rises.
As previously mentioned, when a propellant burns, gases are produced, which are totally contained inside the cartridge case and exert equal pressure on the base of the cartridge, its walls, and the base of the bullet.
In accordance with gas laws, as soon as the bullet begins to move, the volume filled by the gases grows and the pressure begins to decline.
In modern propellants, moderating the propellant grains can compensate for this fall in pressure. This moderation involves the addition of grains. In some propellants, the grains are also pierced with holes.
Different types of powder are discussed below:
Progressive power:
For some weapons, especially shoulder arms, it is preferable for the pressure to build gradually rather than suddenly. When dense and bulk powder is burned, it burns quickly, giving the projectiles a powerful shove. Better velocities are provided by the gradual increase of pressure, which also delays the barrel's fast deterioration.
By regulating the size and form of the powder grains, progressive powders are created to meet the requirements of a certain weapon.
It commences as soon as the first grain of propellant is ignited and Proceeds till the Projectile leaves the muzzle of the weapon.
The study includes all the details concerning the impulse which makes the projectile move out from the muzzle in the air.
As a matter of fact, the projectile obtain its energy during the period it remains in the firearms.
This period can be divided as follows:
- Lock Time
- Ignition Time
- Barrel Time
1.Lock Time:
The lock time is the period of time between the release of the sear and the striker's collision with the percussion cap. Rapid fire is more favourable with a short internal time. There are several techniques to measure the lock time, and one such system makes use of linear motion sensors and an oscilloscope.
2.Ignition time:
The ignition time is the amount of time that passes between the firing pin being struck and the first grain of powder blowing up. In typical circumstances, the ignition takes place at an interval of about 0.002 seconds.
3.Barrel Time:
The amount of time between pulling the trigger and the bullet leaving the muzzle end is known as the barrel time.
In case of most of the weapons Lock time + Ignition time + barrel time varies from 0.003 to 0.007 seconds.
Phenomenon of Internal ballistics:
1.Ignition:
When the firing pin strikes the hammer, the priming compound explodes quickly, creating a jet of flames with a very high temperature that enters the propellant chamber through the flash hole. The propellant, which burns quickly to produce a large volume of high pressure gas and accelerate the bullet down the barrel and out the muzzle end, is ignited by this jet of flame, which has a temperature of roughly 2000°C.
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2.Burning of Propellant:
Nitrocellulose propellants will burn gently if lit in an open area. If it is in a confined location, the heat and pressure created will exponentially increase the rate of burning.
The products of combustion in case of Nitroglycerine are as detailed below:
Nitroglycerine+Carbon dioxide + water Vapours + Oxides of Nitrogen + Nitrogen + Heat
At normal Temperature (0 °C) and Pressure (760 mm), 1 gm of Nitroglycerin will 1000 Cubic centimetres of Gases. The process produces a lot of heat, roughly a thousand calories worth. The temperature may rise beyond 3000 °C. Just a part of this energy is transformed into the projectile's kinetic energy. It is largely squandered.
When used as a weapon, the propellant is contained in a cartridge case with a bullet sealing the mouth. The chamber walls and standing breech of the weapon then sustain the round of ammunition. Under these circumstances, the pressure buildup will continue until it is high enough to overcome the bullet's inertia and cause it to begin accelerating down the bore. The pressure and resistance increase as the bullet weight rises.
As previously mentioned, when a propellant burns, gases are produced, which are totally contained inside the cartridge case and exert equal pressure on the base of the cartridge, its walls, and the base of the bullet.
In accordance with gas laws, as soon as the bullet begins to move, the volume filled by the gases grows and the pressure begins to decline.
In modern propellants, moderating the propellant grains can compensate for this fall in pressure. This moderation involves the addition of grains. In some propellants, the grains are also pierced with holes.
Different types of powder are discussed below:
Progressive power:
For some weapons, especially shoulder arms, it is preferable for the pressure to build gradually rather than suddenly. When dense and bulk powder is burned, it burns quickly, giving the projectiles a powerful shove. Better velocities are provided by the gradual increase of pressure, which also delays the barrel's fast deterioration.
By regulating the size and form of the powder grains, progressive powders are created to meet the requirements of a certain weapon.
Example: Many perforations on powder grains.
Degressive powder:
The shape and size of the grains are maintained in degressive powders in such a way that the rate of burning continues to decrease while the propellant burns.
Example: non-perforated powder grains.
Constant burning propellant:
The powder grains in this kind of propellant have a single hole, and the total surface area burning at any given moment is constant.
Example: Single perforated grains.
3. Geometry of Gunpowder
Degressive powder:
The shape and size of the grains are maintained in degressive powders in such a way that the rate of burning continues to decrease while the propellant burns.
Example: non-perforated powder grains.
Constant burning propellant:
The powder grains in this kind of propellant have a single hole, and the total surface area burning at any given moment is constant.
Example: Single perforated grains.
3. Geometry of Gunpowder
Burning of propellants is a function of geometry of gunpowder; certain terms concerning burning are briefly explained here:
- Combustion: Combustion occurs when a burning substance or propellant reacts to the air it comes into touch with in an open area. If the reaction occurs inside of a closed container, the area should be sufficiently large to allow the heat produced to dissipate and the gases created to disperse without significantly raising pressure. The gradual heating of the surroundings promotes the spread of fire.
- Deflagration: Between slow combustion and detonation, Deflagration is the intermediate stage that includes swift and furious burning. According to the circumstances present in the explosive system, this is brought on by either the acceleration brought on by progressive heating up or the increased pressure of the gases produced by the disintegration of the mass.
- Detonation: This occurs when the explosion is very quick and the gas creation is virtually immediate, causing shock waves, often referred to as explosive waves, to propagate throughout the mass. Ballistic powders have the ability to ignite quickly and in huge quantities, creating high temperature gases. The grains that make up the propellant charge should all be around the same size and shape. As the burning process continues, the area of solid cylindrical grains decreases. Propellers of this form are referred to as continuous burning propellants because cylinders with certain holes throughout their length offer a practically constant surface. When the burning process continues with many holes, more propellant is burnt. In terms of forensics, the latter has a ballistic advantage since it produces gas at a faster rate as the bullet collects velocity and leaves a larger amount of space behind it as it passes through the barrel and approaches the muzzle to escape into the atmosphere.
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4. Combustion of Propellants and Barrel Length
There are wide variations in the rate of burning of the powders. Some powders burn quickly, while other burns slowly. Various firearms require different burning rates. For example, in pistols and revolvers, a very quick burning powder is needed so that the powder is converted into gases before the projectile is pushed out of the short barrel of the firearm. If slow burning powder is used, the projectile will not acquire the desired velocity. Likewise if quick burning powder is used in long barrelled firearms, the projectile will not receive sustained pressure. Consequently, the projectile will move at a slower speed with the highest pressure. The projectile can be given higher velocity for the same maximum pressure if the right kind of powder with the right burning rate is utilised. The length of the barrel must be proportional to the rate of burning.
Beyond a certain point, the pressure inside the handgun cannot be raised. The capacity of the barrel and action of the handgun to sustain pressure mostly determines the limit.
5. Atmospheric Temperature
The ammunition is manufactured to give the desired velocities and pressures at a particular atmospheric temperature. If the temperature differs only slightly at the place of the use, the ballistic aspects are not seriously affected. If temperature variations are substantial (e.g., in Ladakh or in Rajasthan desert), they affect the ballistics aspects of the ammunition.
. In hot places the pressures developed may be excessive and the firearm may burst. In cold places the ammunition may develop low velocities. Indian Ordnance Factories manufacture most of their ammunition with a temperature tolerance of —52°Cto72°C.It has been found that the variation in velocities because of the temperature is about one meter per second per degree centigrade.
6. Shape of the Cartridge Case
It has been observed that if there is an abrupt junction of the neck and the case, the rounds develop greater pressure (for the same quantity of powder). The combustion is more uniform. It appears that abrupt neck joint deflects the hot gases inward. The hot gases quickly ignite the powder charge in every nook and corner. Thus correct initiation and complete combustion of the powder charge takes place inside the cartridge. It reduces excessive heating and wear and tear of the barrel.
7. Heat Problems & Combustion of Propellants:
The temperature frequently rises to 3000°C while propellants are burning. If gases at these temperatures persist in the barrel for any length of time that is significant, the steel barrels of the weapon easily melt at these temperatures. Fortunately, the hot gases only come into contact with the barrel for around 0.001 seconds. As a result, the high temperature does not cause the destruction that might otherwise be anticipated. Instead, the barrel slowly erodes, or "washes," as a result of the hot gases continuing to flow. Metal is removed by them steadily but slowly. The diameter increase has a significant impact on both the aim and the range.
The eroding process happens more quickly with repeating weapons (automatic or semi-automatic). They do not give the barrels enough time to cool down in between rounds. Higher temperatures cause more erosion. The barrel wears out more faster when Nitroglycerine powders are used because greater temperatures are produced.
The firearm's leed of the barrel experiences damage first. A wider lead has a significant impact on projectile accuracy. A portion of the energy is lost since it makes it easier for the gases to escape. Another phenomena seen in the widely used weapons is petrol cutting. At some spots, either as a result of projectile deformation or leed erosion, the hot gases that are rushing out come out as jets, which leave furrows in the ground. During time, these furrows become wider and deeper as a result of the steadily rising quantities of gases that are forced through them.
8. Density of loading & Combustion rate:
An important factor, which affects the rate of combustion, is the density of propellant load. Density of propellant loading is given by the formula, S = u/V*100
Where, u is the volume occupied by the powder, V is volume of the cartridge case
S is the density of loading.
In the rifle cartridge, the loading density varies from 75 to 95.
Greater densities are more advantageous since they allow for homogeneous burning, proper pressure development, economic production, and regular velocities. Little loading densities may cause "hang fire" to occur. The range and aim of a shot are dramatically impacted by improper loading density.
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9. Barrel Fouling:
It happens when hot gases melt metal, which is then slowly and progressively moved from the barrel's base to the muzzle end.
The effects of barrel fouling include reducing airflow, reducing range, and growing the barrel's internal diameter.
The automatic and semi-automatic repeating farms deteriorated more quickly because the barrel didn't have enough time to cool down in between shots.
N.B: The use of nitroglycerin powder result in higher temperature.
10. Gas Cutting:
Another issue with the often used weapons is gas cutting. Due to projectile deformation or leed erosion, the hot gases that are rushing out at specific spots may burst out as jets that plough furrows in the ground. Due to the steadily rising amounts of gases flowing through these channels, these furrows grow wider and deeper over time.
11. Vibration and Jump:
The weapon moves backward and upward as soon as the projectile or projectiles begin travelling ahead. Jump is the name for the barrel's movement. With handguns, there is a notable uptick. A double-barreled firearm experiences side vibrations. The way the rifle is handled has a significant impact on the vibrations and the jump. When compared to the vibrations brought on by the movement of the bullets in the barrel, these vibrations are considerably less intense. As soon as the hammer is released and struck, certain vibrations are produced. The direction of the gun's rotation is upward.
12. Theory of Recoil:
Due to the barrel's position above the hand and, thus, above the wrist's rotational axis, this force also turns the gun upward in addition to driving it to the rear.
When the barrel is lifted and the bullet is moving down the bore during that time, it will hit the target higher than where the barrel was aimed when the trigger was pressed. Although the actual amount of time the bullet spends in the barrel is very brief—on the order of 0.001 seconds—the fact that the muzzle raises the point of aim by a little amount of time does impact the situation. Nonetheless, this does have a noticeable impact on the bullet's striking point and shift the impact point at 100 yards by more than an inch.
References:
1. Firearms and Ballistics; by Brian Heard
2. Internal Ballistics-II; EPG Pathshala
3. Class Notes (NFSU - Delhi)
