Bullets fired through rifled firearms receive both the class and individual characteristics of the barrel from which they are fired. These random and class characters define the characteristics of bullet.
The bullet show the primary markings left behind by the gun barrel’s lands and grooves and reveals the fine striations on all marks. The various class characteristics of bullet include caliber, number of lands and grooves, twist direction, and width of the lands and grooves. Individual characteristics of the bullet include the striation marks present on the bullet.
This article further explains in detail the various class and individual characteristics of bullets.
Class Characteristics of Bullets
Class characteristics of physical evidence are always referred to the properties which can be associated only with a group and not with a single source. The following are the characteristic of bullets which can be classified under the class characters.
1. Number of Lands and Grooves
On discharging a gun, the grooves present in the bore of the firearm cause the bullet to spin as it travels through the length of the barrel. The high pressure created while propelling out the bullet causes the bullet to be pressed and scraped against the rifling. As a result, the fired bullet comprises the characters of the land and grooves.
2. Direction of Twist
The rifling present in the barrel is either twisted to left or right, which in turn causes the bullet to rotate as it passes through the bore, which ensures gyroscopic stability in its flight.
3. Width of Lands and Grooves
It is a characteristic of a bullet that is defined as the distance between the two lands present on the bullet.
4. Pitch and Depth of Lands and Grooves
Depth of the land and groove describes how deep the raised portion of the barrel is to the actual caliber of the firearm. On the other hand, the pitch is the angle of the groove edge concerning the width and steepness of the groove.
All these characteristics of a bullet are the ones that are imparted from a firearm onto the bullet.
The caliber of the weapon is the diameter of the bore of the weapon that is measured from land to land. This class character is also imparted during the making of the bullet.
Individual Characteristics of Bullets
These are defined as the properties of physical evidence that are unique to particular evidence. Striations produced on the bullets due to the rifling are the unique characteristic of a bullet.
The striations are imparted as lands and grooves inside the barrel are imparted along with the striation on the bullets when fired.
The various striation marks found are :
These are defined as the marks found on a fired bullet caused by its contact with the elevated portion of the firearm’s bore. It appears as slight scratches on the body of the bullet.
2. Skid Marks
These are the unique characteristics of bullets found as marks caused when a bullet is fired from a revolver.
3. Stripping Marks
These marks are found on bullets fired from the loose fit barrel where the rifling is badly worn out. The striations in the lands and grooves from a fired bullet provide a direct link to the bore of a particular weapon.
Class characteristics are usually measurable features of a specimen which is restricted to the group of the specimen. On the other hand, individual characteristics are patterns produced by the random irregularities of a tool surface and are unique to a particular specimen.
All these various characteristics of the bullets, including the class and the individual characteristic, helps in determining the firearm from which a particular can be fired, which in turn helps narrow down the perpetrator.