# Why Bullets Spin When Shot From A Rifle Or Handgun?

The spiral grooves (called barrel rifling) inside the barrel of a rifle or handgun cause the bullet to spin. On pulling the trigger, the primer gets hammered and a spark is generated. This small explosion ignites the gun powder and a lot of gas and high pressure are produced. The bullet is forced out due to high pressure and passes through the barrel having helical grooves. These spiral grooves, also known as barrel rifling exert torque and forces bullet to spin.

Quick Question:

Bullets spin when shot from a rifle or handgun. what causes this spinning?

• a) Primer
• b) Action
• c) Rifling ✔️
• d) Cartridge

Answer: c) Rifling, Barrel rifling causes bullets spin when shot from a rifle or handgun.

If you have seen the wanted movie, I am sure you might have noticed a scene in which when a bullet is fired, it starts to spin.

Have you wondered why bullet spins whenever it is fired from a rifle or handgun? Do all bullets spin? Is this spinning of the bullet is intentional?

Let’s answer these questions one by one. The answer to the first question that is why bullet spins lie inside the barrel of the rifle.

## Barrel Rifling

If you cut the barrel of a gun, you will notice there are helical grooves on the internal surface of the barrel.

Whenever the gun trigger is pulled, the primer gets hammered which creates a spark in primer. This small explosion in the primer ignites the gunpowder in the case. The burning of gun powder suddenly generates lots of gas and high pressure gets created which forces the bullet out from one end of the cartridge. Then, the helical groovings inside the barrel exert torque and force a bullet to spin along its longitudinal axis.

This spiral groovings on the internal surface of the barrel are referred to as rifling. It is described by its twist rate which rate of spin in the rifle barrel. It indicates the distance the rifling takes to complete one full revolution. Generally, fast twist barrels are used for longer bullets while slower twist barrels are used for shorter bullets

## Do all bullets spin?

Yes, most of the modern firearms have spiral grooves which cause the bullet to spin. Barrel rifling was invented in Germany in 1498 but it did not become common until the 19th century because the gun powder used earlier used to leave some residue which filled up these grooves quickly and making grooves useless.

Read: ︻┳═一 Can you dodge a bullet?

## Why barrel rifling is done?

Barrel rifling is done to increase the accuracy and range of the bullet. A spinning bullet is more stable because of angular momentum gained due to barrel rifling. It increases the aerodynamic stability and accuracy of the bullet as compared to smoothbore barrels.

## Type of barrel rifling

### Polygonal Rifling:

Traditionally rifling is made up of sharp edge grooves. These sharp edge grooves are replaced by less pronounced “hills and valleys” such that the barrel bore becomes polygonal.

Polygonal rifling has many advantages such as the thickness of the barrel is not compromised, provides a better gas seal around the projectile, less bullet deformation, an increase in muzzle velocity, and an increase in barrel life.

### Extended range full bore:

These types of rifling are used in tanks and artillery pieces in which projectiles have small fins that ride in the grooves of the barrel. It helps to achieve high muzzle velocity and range. Examples of extended range full bore are South African G5 and Germany PzH 2000.

### Gain-twist rifling:

Barrels with gain twist rifling have a slow twist rate that gradually increases with the bore length. There is some evidence that shows that gain twist rifling improves accuracy and delivers more velocity with certain types of bullets and barrels.

## Does the barrel length affect the spin rate of the bullet?

The length of the barrel does not affect the spin rate of the bullet. It helps to increase the velocity of the bullet. The spin rate of the bullet depends on the twist rate of the rifling. The twist rate and velocity of the bullet provide RPM which helps bullet to stabilize. The RPM of velocity can be calculated as

Bullet RPM = Muzzle velocity x 720 / Twist Rate

Therefore, bullets spin when shot from a rifle or handgun because barrel rifling causes this spinning.

References

Professor Atom

Professor Atom is a science enthusiast and alumni of IIT Bombay. According to him, every question can be solved with curiosity and mind mapping. ( Curiosity = Asking Questions = Learning )