Internal Ballistics
Internal Ballistics can be simply defined as the mechanism occurring within a firearm when a bullet is fired. This includes studying the manufacturing techniques of the barrel along with the factors that affect the internal gas pressure and the recoil. It deals with the projectile motion inside the gun after the trigger is pulled until the bullet leaves the barrel of the gun is called internal ballistics. Therefore, the series of events that happens are:
Ignition: The firing pin strikes the primer or percussion cap, igniting the gun powder or propellant and creating enough heat to burn the entire propellant. This burning results in release of gases inside the propellant chamber, which then fills up the bullet's casing through the flash hole. The bullet is propelled down the barrel when the gas pressure, together with the intense heat it produces, exceeds the friction keeping it inside the casing.
Propellant Burning: When nitrocellulose propellants burn inside of a small space, they produce a lot of heat and gas pressure that can reach temperatures beyond 3000°C. The cartridge case contains the propellant, while the bullet seals the mouth.
The bullet then enters the barrel. The rifling, or grooves, in the barrel cause the bullet to spin and gather speed as it travels through the barrel, improving the accuracy of the gunshot.
Following Newton's Third Law "Every action has an equal and opposite reaction", the force that pushes the bullet forward through the barrel also pushes the rest of the firearm backwards, causing recoil. A shock wave of sound and the muzzle flash, are both created, when the burning gun powder departs the barrel and the bullet is rapidly unleashed. The shock wave blast traveling outward moves at a speed that is greater than the speed of sound, known as gunfire. The muzzle flash of larger guns is accompanied by flames.
The different time periods inside the gun can be distinguished as follows:
a. Lock Time; b. Ignition Time; c. Barrel time
a. Lock time:- Depending on the firing mechanism, the lock time of the gun is the period of time from the moment the trigger is pulled until the firing pin contacts the primer. This time is often measured in milliseconds. An oscilloscope and a linear motion sensor system are used to measure the lock The ignition time normally varies around 0.002 seconds and is the time period between the striking of the firing pin and the first blowing of the gun powder.time.
b. Ignition Time: The ignition time, which is the interval between striking the firing pin and blowing the gun powder for the first time, typically fluctuates around 0.002 seconds.
c. Barrel Time: It is the entire amount of time between pulling the trigger and the bullet ejecting from the muzzle. (For the majority of weapons, Lock Time + Ignition Time + Barrel Time = 0.003 seconds to 0.007 seconds.)
In forensics, the Internal Ballistic Examination includes:
1. In cases of accidental fires, the working mechanisms of the firearms are examined.
2. The home-made guns or the zip guns are examined properly to check the proper discharge of the ammunition.
3. A microscopic examination, along with an inter- and intra-comparative comparison, is done among the bullets and cartridges to analyze whether or not the particular firearm was involved.
4. Both empirical (.45) and metric (9mm) measurements can be used to determine the caliber (bullet diameter in casing). The caliber of the bullet informs you of the force of the recoil and the capability of the ammo to stop an object. If a bullet is shot from the same gun or not, it aids in matching
By Himika Ghosh