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Uses of Mobile Application in Crime Scene Investigation

Forensic Ballistics- Firearms and Its Parts (What are the various parts of a firearm?)

By,

Dr. Bhoopesh Kumar Sharma
Forensic Expert & Associate Professor

In our last post we have discussed about the brief introduction of forensic ballistics and ballistics. Let us move ahead in the section and understand the basics of the firearm and its parts.

What is Firearm?


A firearm is a device through which, with great force, a single projectile or projectiles can be hurled. The force is given by gas expansion, usually produced by propellant burning. As we have discussed in the anatomy of the cartridge (ammunition) that propellant is the main charge (gun powder) that results in enormous amount of heat and gases during combustion. This expansion of the gases is used as the force to hurl (propel) a projectile or projectiles from the firearm. A firearm is an assembly that a person uses to project a projectile toward the target. It is the machine which, with the release of heat, light and pressure, converts the potential energy of the primer and the propellant charge to kinetic energy. This kinetic energy is utilized to hurl the projectile. The amount of kinetic energy released depends upon the nature and amount of propellant charge used. 

Pistol

Parts of firearms
Picture Showing Various Parts of a Firearm


Major Parts of the Firearm:- 


1. Barrel: - It is the part of a firearm in the form of a hollow cylindrical tube through which the projectile is projected out of the chamber or the Action block of the firearm and leaves the barrel. It is divided into two main parts, the distal end known as the Muzzle and the proximal end known as the Breech. The modern firearms are the breech loaders i.e. the cartridge is inserted or loaded from the breech end of the barrel.

Picture Showing Parts of the Barrel of Gun


It is usually a steel tube that is used to house the cartridge and provides space for the expansion of the gases during firing. The breech end is provided with an extractor to remove the empty cartridge case after firing from the chamber of the firearm. The length and the diameter of the barrel differ from firearm to firearm on the basis of their caliber size, make and model. For example: - a revolver is a short barrel gun whereas a rifle is a long barrel gun.


2. Action or Breech Block: - It can be considered as the heart of the firearm as it is the one responsible for overall firing mechanism from loading to the extraction of empty cartridge case. It consists of mechanism for loading of live cartridge inside the chamber, breech block, firing pin, extraction mechanism, trigger and magazine. There are various types of Action Mechanisms used in different types of firearms such as: - Dropping block, Tilting block, Falling block, rolling block, Break-action, hinged block, Bolt action, lever action, Pump action mechanism etc. break action is a type of firearm where the barrel(s) are hinged and can be "broken open" to expose the breech. The breech is a metal made block that seals the breech end of the barrel (chamber) when the firearm, is closed and ready to fire.  As soon as the trigger is pressed it releases the firing pin in turn which hits the percussion cap of the cartridge base and initiates the firing. The marks produced by the firing pin and the breech block on the fired cartridge case serves as a mean of identification of the firearm in firearm cases.

Picture of a Bold Action Gun

Picture of a Lever Action Gun
3. Butt Stock: - It is grip provided with the firearm. It holds the parts of the firearm in their position. It is used to hold the firearms sophisticatedly. The size and shape of the butt stock depends upon the size of the firearm and the barrel as in case of long barreled firearm the butt stock is shaped to fit on to the shoulder whereas in case of handguns it is gripped in hand. It may be made up of wood or metal & may have space to accommodate the magazine loaded with cartridges in some automatic firearms.

Classification of Firearms: 

In a broader sense the Firearms are classified according to their bore characteristics i.e. Smooth bore firearms and Rifled bore firearms. The smooth bore firearms are those having an uniform smooth internal lining (bore) of the barrel (as discussed in previous post) where as the rifled bore can be defined as those which are having grooving inside the barrel.

There are several classifications given to firearms on various basic grounds such as: -
  1. The barrels (the bore characteristics): - smooth bore and rifled bore firearms
  2. The action mechanism: - lever action, bolt action, self-loaders and automatics.
  3. The firing characteristics: - single shots, repeaters.
  4. The handling characteristics: - handguns and shoulder arms.
  5.  Use: - sporting firearms, service fire arms.


Firearms on the basis of the firing mechanism are divided in to three main categories i.e.:-

  1. Manual Firearms: - These are those firearms which need loading and reloading of the chamber after each firing and can fire only one cartridge at a time.
  2. Semiautomatic Firearms: - These are the firearms where several cartridges are loaded at one time and a repeated firing is done one after the other by pressing the trigger for each firing.
  3. Automatic firearms: - These are the firearms those fires continuously few to hundreds of cartridges at once by pressing the trigger the once.

Description of Some commonly used firearms firearms: - 

Rifle

Rifles differ from short guns or handguns in the length of the barrel and the presence of a butt stock. They are harder to carry and more loosely regulated than handguns. However, they are much more accurate and shoot more powerful cartridges than handguns. Rifles may be manufactured as single shot, but most commonly are bolt action, used for large caliber hunting rifles. Military rifles are semiautomatic or automatic, having a detachable magazine holding 5 to 50 rounds. Pump action and lever action rifles, usually of lower caliber, have magazines below the barrel.


Rifling is actually the grooving in inside of the barrel during the manufacturing process and imparts the lands and the grooves to the barrel which is not present in case of the smooth bore firearms or shotguns and also in most of the country made firearms. The rifling spirals down the inside of the bore and impart spin on the bullet as it travels down the barrel. This spin contributes a great deal to the accuracy of modern firearms.

By measuring the distance between the two opposite lands of the rifling inside the bore, one can determine the caliber of a firearm. This measurement, which is usually less than one inch, is commonly measured in hundredths of an inch. For example, a 30 caliber bullet would correspond to .300 inches. Caliber can also be measured in millimeters. For instance, a 9mm handgun has a 9 millimeter bore diameter. It is important to note that barrels are made for a specific caliber, but also chambered for a specific cartridge. 

Rifling provides a steady uniform and gyratory (spinning) motion to the projectile during flight. The gyratory motion has following important effects on the bullet:

       It stabilizes the bullet flight with nose on position
       Increases the effective range of firing
       It decreases the air resistance.

Some examples of the rifled weapons are Rifles, Revolver, Pistols, and Machine Guns etc.

Revolver

The name revolver is termed due to the presence of a revolving cylinder bearing the cartridges to be fired in a circular motion. Each cartridge is placed in the front of the firing pin with the help of the action mechanism and ready to fire one after the other. A revolver has several advantages and unique features. Importantly, they are less expensive, simpler in design, and more reliable than other firearms. On the bad side, revolvers are limited to six or several shots are relatively slow to reload, the gap between barrel and cylinder makes them less efficient, and the trigger pull is greater. 

revolver diagram

Barrel length is smaller for concealability and longer for accuracy or energy. The ejector rod under the barrel is used to eject fired cartridges before reloading. Sights on a revolver are usually a blade in the front and a notch on the rear. The frame is the largest part, and all other pieces attach to it. Frames are usually made of blued or plated steel, stainless steel, or lightweight alloys. A revolver may weigh less than 1 lb to more than 4 lbs. The cylinder contains five or six holes for the cartridges and can be swung out for easy reloading. This must be a conscious act, so that no empty cartridge cases will be found at a crime scene unless the assailant stopped to reload.
There is a gap between cylinder and barrel to allow the cylinder to turn freely, but this also allows gases to escape laterally, which at close range may deposit gunshot residue on surrounding structures and allow the forensic expert to reconstruct the scene. 

Pistols: -

In this type of firearm when a cartridge is fire, the empty cartridge case is thrown out and a new cartridge slips in to the breech of the barrel automatically with the help of a spring mechanism. The other cartridges are contained in a magazine placed vertically in the firearm in its stock that can accommodate several cartridges in it. They are actually the semi-automatic or self-loading because the trigger has to press each time when a round is fired. This is more conducive to firing multiple shots, so many are designed to carry 15 to 19 rounds. The major disadvantages of these firearms include a more complicated mechanism; require more practice to use, and cartridge cases must be short to work well. The barrel is normally hidden by the slide. 


The slide is able to move back along the axis of the barrel under tension from a spring. Since the cartridge base rests on the slide, the slide does just that under the force of recoil generated by the firing of the cartridge. As the slide and empty cartridge case are accelerating backwards, the case is struck by a stationary piece of metal that bumps it to the side. This is conveniently located next to a hole in the slide, so that the empty cartridge case continues its acceleration in a direction perpendicular to the pistol and into the air, landing from 2 to 20 feet from the fired gun. The rearward- moving slide also cocks the hammer. After the case is clear the slide hits a stop and the spring tension starts it forward. The magazine spring is pushing on a column of rounds tight up against the bottom of the slide. As the slide comes back by the column of cartridges, it grabs the top one and pushes it forward and up a short ramp into the chamber where the slide locks it in place.

The handle, or butt, is more important here because it contains the magazine holding the cartridges. Safety mechanisms prevent accidental firing. Some lock the hammer, while other designs lock the trigger.
Even on open ground ejected cases may be difficult to find, as they typically roll into a hiding place such as grass or small depressions in the ground. Thus, ejected cases will virtually always be left behind at the scene, but must be searched for diligently.



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