# How Fast Does a Bullet Travel?

By: Yara Simón  |

How fast does a bullet travel? And what would happen if you fired a gun on a train moving as fast as a typical bullet? The latter is a particularly good question because it involves the concept of reference frames.

The quick answer is that, relative to you, the bullet will always travel at the same speed. In other reference frames, however, unexpected things can happen!

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## Firing a Speeding Bullet on a Speeding Train

You may have heard of Newton's first law:

"Every body persists in its state of rest or of uniform motion in a straight line unless it is compelled to change that state by forces impressed on it."

We tend to rephrase this a little and say that a body in motion tends to stay in motion and a body at rest tends to stay at rest unless acted on by an external force.

###### Applying Newton's First Law to Physical Objects

Imagine you are on a perfectly smooth speeding train, moving at a uniform speed (not accelerating or turning), in a car with no windows. You have no way of knowing how fast you are going (or if you are moving at all).

If you throw a ball straight up in the air, it will come straight back down whether the train is sitting still or going 1,000 mph (1,609 kph). Since you and the ball are already moving at the same speed as the train, the only forces acting on the ball are your hand and gravity. So the ball behaves exactly as it would if you were standing on the ground and not moving.

What does this mean for our gun?

If the bullet leaves the gun at 1,000 mph, then the bullet will always move away from the gun at 1,000 mph (1,609 kph). If you go to the front of a train that is moving at 1,000 mph (1,609 kph) and shoot the gun forward, the bullet moves away from you and the train at 1,000 mph (1,609 kph), just as it would if the train was not in motion.

But relative to the ground, the bullet will travel at 2,000 mph (3,219 kph), the speed of the bullet plus the speed of the train. So if the bullet hits something on the ground, it will hit it going 2,000 mph.

If you shoot the bullet off the back of the train, the bullet will still be moving away from you and the gun at 1,000 mph, but now the speed of the train will subtract from the speed of the bullet. Relative to the ground, the bullet will not be moving at all, and it will drop straight to the ground.

###### The Physics of Sound Waves

What's true for the average bullet, however, is not true of some other things that you might "shoot" from the front of the train. A great example is sound waves.

If you turn on the stereo in your living room, sound waves "shoot out" of the speaker at the speed of sound — something like 700 mph (1,127 kph). The waves propagate through the air at that fixed speed, and they can go no faster.

So if you put a speaker at the front of the 1,000 mph (1,609 kph) train, the sound waves will not depart the train at 1,700 mph (2,736 kph). They cannot go faster than the speed of sound. This is the reason why planes traveling faster than the speed of sound create sonic booms.

## Factors That Influence Muzzle Velocity

Muzzle velocity is the speed of a bullet as it leaves the firearm's barrel. It is the initial velocity imparted to the bullet, and it varies significantly depending on several factors, such as:

• Barrel length: The speed of a bullet depends, at least partially, on the length of the firearm's barrel. Longer barrels, like those on rifles, generally provide more space for the propellant gases to accelerate the bullet, resulting in higher speeds.
• Air resistance: Air resistance or drag acts as a retarding force that opposes the bullet's motion. The shape and design of the bullet influence its ability to overcome this resistance.
• Bullet weight: Bullet weight can also affect muzzle velocities. Typically, lightweight bullets travel at higher initial velocities compared to heavier projectiles.
• Cartridge type: The type of cartridge used, such as a rimfire cartridge or centerfire cartridge, can affect bullet speed.
• Gas pressure: The gas pressure generated upon firing influences the bullet's speed. Higher gas pressures often result in a high velocity.

The are other factors that can also affect the speed at which a bullet travels, such as the type of gun. For example, a bullet fired from a rifle, which has a longer barrel, can reach a higher velocity than a handgun.

Even firearms of the same caliber might have different lengths or designs, which can affect bullet velocity. And different types of ammunition, which include cartridges, propellant and primer, can offer various bullet speeds.

This article was updated in conjunction with AI technology, then fact-checked and edited by a HowStuffWorks editor.