Bullets vs. Arrows: Which One Penetrates Sandbags?

Sandbags have historically proven to be very effective objects at stopping bullets in their tracks. Used for this purpose since at least around the late-18th century at the Siege of Ninety-Six, they are still widely used today for the very same purpose. 

But, can they stand up to the punching-power of arrows? The answer, it turns out, might just surprise you.

But, before we actually look at the different ways bullets and arrows interact with sandbags, it might be useful to compare the two projectiles. 

How do arrows and bullets differ from one another?

If you are familiar in any way with bullets and arrows, you will know that the difference between them is pretty pronounced. Apart from their overall size, shape, and means of propulsion, they both interact with targets in very different, yet at the same time, somewhat similar ways. 

However, it is important to note that this kind of comparison is very much like comparing apples with oranges. They are both different technologies designed for different purposes. 

That being said, let's look at some major differences between them.

1. They are designed for different purposes

As previously mentioned, the main difference between bullets and arrows is what they are designed to do. Arrows, on the whole, are designed to cut through targets using their mass and sharp point, while bullets are designed to deliver massive energy transfer to a target on impact. 

This affects not only how each travels through the air, but what happens when they impact something at the other end. 

This is what tends to make bullet impacts so devastating. Whether it be exposed flesh or a solid object, bullets will tend to cause a serious amount of damage. Arrows, on the other hand, generally drill through and then become lodged into a target. 

2. They have different physical and aerodynamic properties

Bullets are, usually, small metal projectiles fired at high velocity as the result of a controlled explosion. Arrows, on the other hand, are basically lengths of material (like wood, metal, or carbon fiber) with a strong tip (usually metal) propelled from what is essentially a large spring to reach a target. 

This difference is that being launched directly impacts the arrows' design and aerodynamic properties. 

One of the main differences is the way they travel through the air. Bullets have higher velocities and lower mass, and thus, they can travel further and faster than arrows. If the gun barrel is rifled, the bullet will also spin through the air, reducing deviation, making them pretty accurate over distance.

Arrows, on the other hand, react to the extreme pushing forces applied to them as they leave the bow. For this reason, they need to flex around the bow handle as they are fired and then straighten up in flight — this is one of the main reasons why multiple civilizations felt the need to add the fletchings (or fins) at the back of the arrow. 

In-flight, fletchings will stabilize the shaft by imparting a spin on the arrow. This works in a similar fashion to a quarterback giving the football a spiral spin when they make a pass. The spinning action keeps the arrow on its flight path and helps preserve its speed, accuracy, and ultimate impact energy. As a general rule of thumb, the fletching will need to wider than the cutting diameter of an arrowhead.

Arrows will also tend to "wobble" as they fly through the air. The lower launch velocities, and their larger mass, also tend to mean that arrows have a much-reduced range when compared to bullets. 

While both will travel in an overall parabola in flight, arrows are influenced to a far greater extent by gravity, wind direction, and air resistance relative to bullets.

Bullets are also shorter, with broader cross-sections and no fins. Arrows are obviously longer, with smaller cross-sections, have fins to the rear and mass to the front. 

The main reason for this is that bullets need to form a tight seal in the barrel of the gun prior to being fired. This is to maximize the amount of energy transferred to the bullet when the gunpowder explodes, we want to minimize the gases "leaking" around the bullet. For this reason, they tend to be roughly cylindrical or spherical in form. 

3. They actually have relatively comparable momentums, but very different kinetic energies

Any discussion of this nature will typically mention the relative momenta of either bullet or arrows. While a useful metric under some circumstances, it can be a little misleading in the discussion of their relative effectiveness as weapons. 

However, since momentum is a function of the velocity and mass of a projectile, you can probably see the problem with this comparison straight away.

By way of example, compare a 180-grain (11.7 g) bullet being fired at 2000 feet per second (610 m). If compared to a 7000-grain (453 g/one pound) of cotton fiber traveling at 50 ft/s (15 m/s) their relative momentum will be comparable. 

Is this a good metric to use? Obviously not. 

For this reason, it might be better to use another metric like kinetic energy. Unlike momentum, kinetic energy increases as a factor of the square of the velocity of a projectile. 

Given the same examples above, the bullet would have a kinetic energy of about 2,160 joules (1,600 ft/lbs), while the bag of cotton would have about 54 joules (40 ft/lbs). A much bigger difference, and a comparison that is more useful when comparing the two as actual projectiles.

To put those numbers into perspective, a joule is roughly the energy needed to lift an apple 1 meter vertically.

All well and good, but what about an arrow?

Given a 400 grain (26 g) arrow, with a 100-grain (6.5 g) broadhead, traveling at 250 ft/s (76 m/s), the arrow would have a kinetic energy of 94 joules (69.5 ft/lbs). This is clearly a lot less than the bullet example above. To provide the same amount of kinetic energy, it would take an arrow of roughly 2.2 pounds (1 kg) in weight, or velocity in excess of 1310 ft/s (400 m/s) to be comparable.

This is obviously not going to be possible with a regular bow. 

However, it is possible to have too much of a good thing when it comes to kinetic energy — especially when talking about penetration. Higher velocities, and therefore momentum, can be counter-productive, leading to the projectile shattering on impact and not penetrating. 

Penetration, in abstract, is effectively what happens when two materials contact one another. How either material deforms, the speed of the incoming projectile, and the nature of the target, are all variables that dictate how deep, if at all, the projectile will penetrate. 

This is actually a very complex relationship and can require some fairly complex calculations to predict. 

4. They interact with targets in different ways

Arrows and bullets behave very differently when they hit things. By way of example, let's see what happens to them when they hit a soft target — like a body. 

Let's start with bullets. When they hit a target (depending on what the bullet is made of) their high kinetic energy will tend to cause the bullet to deform on impact. They may even "spin" as they travel through the target.

But is it important to note that some bullets, like armor-piercing rounds, are designed to not deform as much as others, in order to maximize their penetrating potential (hence the name). Others, like hollow-point bullets, are also specially designed to deform in order to increase the transfer of kinetic energy to a target and inflict more severe wounds. 

If hitting a human or animal, the flesh absorbs a large amount of the momentum of the bullet on impact, but not all. This energy needs to go somewhere, and so a large cavity tends to form, which subsequently collapses again. This action causes massive damage to soft tissues, and can even shatter bone. 

But that is not the end of the story.

Bullets can take one of many paths as they travel through flesh, depending on the impact angle and where the bullet hits. This can cause bullets to deviate widely from their original trajectory by being deflected inside the body. This, coupled with their tendency to deform, causes massive damage to soft tissues, and can potentially damage several vital organs in a single shot. 

Not only that, but if the bullet's velocity is high enough (depending on grain size and gun caliber), the bullet can even pass right through a target, leaving a gaping exit wound as it leaves the body. 

All of this causes massive internal trauma, severing blood vessels and leading to internal bleeding, along with external blood loss from bullet entry and exit wounds. Pretty gruesome. 

Arrows, on the other hand, have relatively lower velocities and kinetic energies than bullets. However, they are much heavier, longer, and more robust as projectiles when compared to bullets. 

Unlike bullets (depending on their design), arrows are usually not designed to deform on impact. This means that all that mass behind the arrowhead can be used to "drive" the head deep into a target. This means they are less likely to deviate from their original trajectory and will become lodged in the target. 

If the arrow has enough kinetic energy and doesn't impact a more solid target on impact, it can also fully penetrate and exit a soft enough target too. It is for this reason, under some circumstances, that arrows can be more effective at penetrating things than bullets (more on this later). 

Arrowheads come in a wide variety of shapes and sizes, each designed with a specific purpose in mind. For example, broadhead arrows are effectively very sharp razor blades in a wedge shape that are designed to cut through flesh and bone and cause severe internal damage. 

Others, like bodkins, are streamlined heads specifically designed to focus the arrow's momentum into the smallest area possible in order to penetrate tough targets like armor or chainmail. 

Are bullets or arrows better at penetrating things like sandbags?

And now to the main event, and the reason you clicked on this article. Which of the two, bullets or arrows, will penetrate sandbags? 

Sandbags, as you are probably aware, are a common material used to protect security or military personal from being shot by bullets. This is for a very good reason.

On the whole, small firearm bullets will not penetrate them. Given the apparent fragile nature of sandbags (basically a bag filled with sand or soil), this seems to be a very unexpected outcome on the surface. That being said, with higher caliber rounds, one sandbag may not be enough to block the bullet, but several layers of them certainly will. 

Since bullets travel at very high speeds and have so much kinetic energy, surely they should pass right through? However, as we know from experience, this does not happen. If you don't believe us, check out one of the many demonstration videos online. 

But why?

The main reason is that the friction caused by the sand (or soil) grains within the sack, and the tiny air gaps between them, work as excellent dissipators of explosive energy — like the energy from a bullet. When the bullet impacts the bag, sand particles vibrate against one another and convert the bullet's energy into sound and heat energy.

The friction between the grains also imparts an enormous amount of drag on the traveling bullet, slowing it down very quickly and bringing it to rest. In this respect, the sand also acts as a kind of fluid, which often results leads to the bullet diverting trajectory inside the bag. The sandbag, in effect, acts as a basic form of shock absorber, robbing the bullet of its main method of penetration. 

Sandbags are so effective at this in fact, that they are regularly used as a cheap form of temporary anti-bullet fortifications all around the world. Some bulletproof vests also include small ceramic beads encased in a fabric casing only a few cm thick. 

All well and good, but what happens when you fire an arrow at a sandbag? 

Amazingly enough, the slower, heavier, and less energetic arrow will often, though not always, penetrate the sandbag. Tod's Workshop has an excellent comparison video of just this. 

Still, why?

This is where the arrow's physical characteristics give it a massive advantage over bullets. Their long streamlined shape and sharp point enable them to cut through the sandbag.

The same properties of the sand that slow down and stop a bullet, also impact the arrow too, but since the arrow is being driven in by its larger mass, spring, and wobble, the arrow is able to cut its way through. Depending on the power of the bow used to deliver the arrow, they can even cut clean through sandbags under the right circumstances. 

Another advantage the arrow has over the bullet is its flexible shaft. The tensile strength of the shaft and its length prevent the arrowhead from being deflected inside the sand, enabling the arrow to travel through the sand in a more linear direction. However, with a large enough sandbag, it is conceivable that a similar deflection would also occur to the arrow — as seen with bullets.

This means the arrow can use more of its energy to travel through the bag — thus maximizing its penetration. 

Can sandbags be used to help protect armored vehicles, like tanks?

Since sandbags stop bullets, why don't we use them as armor on things like tanks? As it turns out, they actually were used for this in the past — sort of. 

While anti-tank shells are much larger and more powerful projectiles than small arms, sandbags could, in theory, help take the "sting" out of the shell to help protect the tank underneath. However, this wasn't the main reason for their use. 

During WWII, sandbags were commonly strapped to the front of allied tanks to help protect them against German anti-tank weapons, like the Panzerfaust. The soft-armor provided by the sandbags helped to absorb much of the initial "shock" these devastating anti-tank weapons were designed to deliver.

At least that was the theory.

The actual effectiveness of these sandbags has since been questioned, and they may have provided more of a psychological boost to tank crews than actually protecting them in combat. It has also been suggested that large amounts of sandbags strapped to the front of tanks were also something of a hindrance.

The added weight would often result in more frequent breakdowns of tanks. However, some other historical sources do not seem to support this. 

Can arrows penetrate bulletproof vests?

Since arrows can penetrate sandbags, you might be wondering what other things they can penetrate. How about bulletproof vests?

As it turns out, several experiments have been conducted on just his subject. 

Amazingly, under certain circumstances, arrows can, indeed, penetrate bulletproof vests. This all depends on elements like the thickness and composition of the vest, the power of the bow, the type of arrowhead, and various other factors. 

For example, Kevlar (a common material used in bulletproof vests) vests are specially designed to distributing blunt force impact from bullets across the entire armor piece (as much as possible). By doing this, minimizes the amount of energy from the bullet at the point of impact — hopefully saving the wearer's life. 

This occurs because the fibers of the vest prevent the bullet from forcing its way through the weaved fabric. 

However, arrows are very different pieces of technology. If the same piece of bulletproof armor were to be hit by an arrow with enough kinetic energy, and the right kind of arrowhead, it could penetrate the vest fairly easily, by effectively stabbing through it.

The arrowhead can basically cut its way through the fibers — a feat most low-caliber bullets cannot accomplish. 

As it turns out, Kevlar vests can also be vulnerable to knife attacks, for much the same reason. High-velocity rifle rounds will also tend to easily penetrate this kind of vests. 

But, this is not a very fair comparison, as Kevlar body armor of this kind is only really designed to resist small handguns. Higher quality bulletproof vests of the kind worn by frontline combat soldiers will tend to also include metal, ceramic, or plastic armor plating for this very reason. 

These kinds of high-end bulletproof vests (like the US National Institute of Justice (NIJ) Standard VI) will likely also be very effective against most arrows — even war arrows shot by a longbow. It would hurt, but the arrow shouldn't penetrate. 

So, why were bows and arrows replaced by bullets?

Given the advantages arrows seem to have over guns and bullets, you might be wondering why they fell out of favor in combat? 

The answer is actually quite interesting and has little, if anything, to do with their relative penetration. 

Archers and their equipment take a very long time to make and master. The average medieval English archer, for example, would take years to train to build up the strength and skill needed to reliably and rapidly use bows and arrows in combat. 

Bows and arrows would also need to be crafted by specialist tradesmen. These trades would also require lengthy apprenticeships and years of experience to master. 

Guns, on the other hand, could be made to a standard template and required much less training to wield and fire competently — usually taking just weeks to months. Their ammunition was also relatively quick and cheap to make en masse, compared to arrows. 

However, it is important to note that relative claims of the training required for either weapon are hotly debated. 

For these reasons, among others, guns would slowly become favored over time when compared to bows and arrows. This is especially true when repeating firearms, rifled barrels, and other improvements were made making guns far more potent weapons of war. 

While they may be less effective against sandbags, guns and bullets are also far more useful in other situations when compared to bows and arrows. They are cheaper to make, quicker to learn, can be fired at a faster rate, and over a longer distance than arrows. 

That being said, if you find yourself needing to hit a target behind some sandbags in the future, you might want to put down the rifle and grab your trusty longbow.