What is Rifling? Why its needed and types of rifling

Rifling refers to construction of helical groves inside the barrel of the firearms, which imparts a spin to the projectile fired, throughout the longitudinal

FORENSIC SCIENCEFORENSIC BALLISTICS

Shubham Kumar

1/29/20245 min read

Have you ever wondered why a 12 bore shotgun is just used for hunting, whereas, AK-47 is used in war zone, when both of them have strong projectiles and long barrel. The difference is rifling. Because of rifling, rifles are most used firearms, despite shotguns have even long barrel then rifles.

In this article we are going to get information about the rifling, its purpose, its characteristics, its importance and its various manifestations.

Rifling | Definition

Rifling refers to construction of helical groves inside the barrel of the firearms, which imparts a spin to the projectile fired, throughout the longitudinal axis of the barrel. The rifling is found in various firearms like rifles (M1 Grand, AK 47, Inass etc) and Handguns (Pistols).

Rifling consists of a series of spiral grooves cut into the inside surface of the bore of the barrel
and are there to impart a spin to the bullet through its longitudinal axis. This gyroscopic effect
stabilizes the bullet during its flight, preventing it from tumbling end over end and losing its
accuracy. Rifling in a barrel consists of lands and grooves. The lands are raised portions and the
grooves are present in low spots.

Characteristics of Rifling

The rifling imparts the spin to the projectile fired by firearms. During the flight of projectile from the breach end to the muzzle end, it undergoes into continues spinning, followed by proper accuracy and stability.

Lands and Grooves are the high and low point in the bore of barrel respectively. They are responsible for the spinning of projectile. Due the presence of Lands and Grooves, the striations marks are present of the fired bullet. Through investigation of these striation marks, we can identify the type of weapon used.

No two rifled barrels will have identical striation marks on their fired projectile. It doesn't matter whether they belong to same company, same type or manufacture in succession. These striation marks are the fingerprints of firearms, therefore, No two rifled barrels will have identical striation marks.

Purpose of Rifling

Rifling provides the stability to the flight of projectile, thus enhancing the accuracy to hit the target.

The striation marks produced on the fired projectile due to rifling, is unique on its one. Therefore, it will be very easy to track the weapon type and location through analysis of striation marks on projectile. Hopefully, the person who fire it will also get tracked.

Rifling cause bullet to spin when it comes out. This makes the bullet fly straighter and thus improve accuracy.

Rifling enhances the aiming ability of the projectile to hit the target in desired area.

Importance of Rifling

Rifling, the spiral grooves inside a firearm barrel, imparts a crucial spin to the projectile as it travels down the barrel. This spinning motion, known as gyroscopic stability, has several significant advantages:

Gyratory Motion to Projectile

Rifling imparts a gyroscopic motion to the projectile, stabilizing its flight. This stability prevents erratic movements, ensuring a predictable and accurate trajectory from the firearm to the target.

Higher Velocity

The gyroscopic effect created by rifling allows projectiles to achieve higher velocities and travel over longer distances accurately. The spinning motion adds forward momentum to the projectile, increasing its effective range.

Prevents Wobbling of Projectile

The gyroscopic effect created by rifling allows projectiles to achieve higher velocities and travel over longer distances accurately. The spinning motion adds forward momentum to the projectile, increasing its effective range.

Helps to strike at nose on Position

Rifling helps the projectile maintain a nose-on position, meaning it strikes the target head-on. This orientation maximizes the projectile's effectiveness upon impact, whether it's for target shooting, hunting, or military applications.

Increase the range and accuracy

Due to rifling, the fired bullet gets an ability to counter the air resistance and overcome to wobbling effect, which automatically increases its accuracy and range. Do to stability during its flight, the bullet dose not lose from its path of flight and covers more distance than that of bullet fired from the smooth bore.

Decrease air resistance due to gyratory motion

The gyroscopic motion reduces air resistance as the projectile travels through the air. The stabilized flight minimizes drag, allowing the projectile to maintain its velocity and trajectory, leading to better accuracy.

Gives effective striking velocity

The combination of the rifling-induced spin and the projectile's forward velocity results in an effective striking velocity upon impact. This impact velocity enhances the projectile's penetration power and overall effectiveness.

Trajectory obtained remains flattered comparatively

Better Aim at Longer Distance

Rifling ensures that the projectile's trajectory remains flatter and more predictable over extended distances. This characteristic is vital for long-range shooting, providing shooters with a higher probability of hitting the target even at considerable distances.

Creates a unique mark on the bullet

Rifling refers to the spots present in the whole barrel within which the bullet is being fired. When a rifled bore fires a bullet, the bullet has to pass though the rough inner surface of the barrel. These rough surfaces leads to deformation of bullet's edges, causing to leave unique marks. Forensic ballistics experts analyze these straited marks in order to determine that the particular bullet if fired from the particular firearm. No two firearms can leave the same straited marks on the bullet, these marks are commonly called as the finger print of the firearms.

Types of Rifling

There are two types of rifling

  • Standard- In standard rifling, the series of alternating high and low spots are present. These alternative high and low spots are commonly called as lands and grooves.

  • Polygonal- In polygonal rifling, the series of less pronounced shapes in shape of hills and valleys. These are commonly called as hills and valley rifled bore.

Note: For a rifling to work, the rifling in side the barrel should be small enough in dimeter as compared to that of bullet, so that, bullet can pass smoothly, while receiving, slight straited marks on its surface.

Twist Fate in Rifling

Rifling is characterized by its twist rate, that is, the distance the rifling takes to complete one revolution. For example, if a rifling covers one revolution in 15 inches, that its twist rate will be 1:15.

The twist rate is very crucial in ensuring the gyroscopically stability of the projectile. The combination of length, weight and shape of the projectile determine the rifling of a firearm. This is only the reason why every firearm has different rifling, because they have different projectile. For example, a 7.65 caliber bullet can be fired from 9mm pistol, therefore, 7.65 caliber pistol will always have different rifling than that of rifling in 9mm pistol.

A projectile with large diameter spherical lead ball require a low twist rate, i,e 1:48, which suggests 1 turn in 48 inches. On the other hand, barrels with long length but small diameter projectiles (like 80 gr (0.223) inch bullet) use high twist rate of 1:8, that is 1 turn in 8 inch or faster.

In some cases, rifling will increase the twist rate as projectile travels down the length of barrel called gain twist or projectile twist.

Reference

  • "Forensic DNA Typing" by John M. Butler

  • "The Forensic Casebook: The Science of Crime Scene Investigation" by Ngaire E. Genge

  • "Forensic Science: A Very Short Introduction" by Jim Fraser

  • "Practical Crime Scene Processing and Investigation" by Ross M. Gardner