Hollow-point bullet

Some bullets have a hole in the tip.

When these bullets hit something soft, the hole changes. The metal pushes out to the sides. This makes the tip wide like a mushroom.

This shape helps the bullet stop quickly. It does not fly too far through a target. This helps keep people nearby safe.

People use these for target shooting, too. The shape helps them be more accurate. They are good for many jobs.

A hollow-point bullet has a hole in its tip.

When this bullet hits a soft target, it changes shape. The pressure from the impact pushes the metal outward. This makes the tip wide and rounded. People call this mushrooming because it looks like a mushroom.

This shape helps the bullet stop quickly. It transfers its power into the target. Because it stops, it is less likely to fly through and hit something else. This helps keep people nearby safe.

Some bullets have a jacket. A jacket is a thin layer of hard metal like copper. It wraps around the soft lead core. This makes the bullet stronger. It also helps the bullet fly better.

Some makers add plastic to the tip. This plastic helps the bullet expand reliably. In target shooting, these bullets can be very accurate. The flat tip helps the bullet fly in a steady way.

A hollow-point bullet is a special type of projectile designed to change shape. Most bullets are solid, but these have a hole in the tip.

This design is important for safety and control. When a bullet hits a soft target, it expands to use up its energy. This prevents the bullet from going through the target and hitting something else nearby. This is called controlled penetration.

It is very useful in places like an aircraft where you cannot have objects flying through walls.

How does this expansion work? When the bullet strikes a soft object, pressure builds up inside the hollow cavity. This pressure pushes the metal, usually made of lead, outward from the inside. The bullet's diameter increases as it passes through the target.

This process is often called mushrooming. It gets that name because the widened, rounded nose looks like a mushroom. This new shape creates more surface area. This extra area helps the bullet stop faster and transfer its energy more effectively.

History shows that these bullets have changed a lot over time. Long ago, soft lead bullets would sometimes deform on their own. In the late 1800s, people began making hollow-point bullets called express bullets. These were meant to be lighter and faster.

Later, around 1890, new designs were made at a British arsenal in Dum Dum, near Calcutta. These were called jacketed hollow-points because they had a hard metal skin. This skin helped the bullet stay strong while flying at high speeds.

There are many different ways to build these bullets today. Some have a jacket that is thin at the front to help it expand easily.

Others have parts inside the core to stop the expansion at a certain point. Some even use plastic tips to help the bullet fly better through the air.

Scientists and testers use a material called ballistic gelatin to see how they work. They measure how wide the bullet gets and how deep it goes. This helps them know if the bullet will work for hunting or police use.

Because these bullets can cause serious injury, they have special rules. The Hague Convention of 1899 prohibited using them in international warfare. This was because they can cause unnecessary suffering. However, they are very common for civilians and police. They are used because they are less likely to hit bystanders. In some places, like the United Kingdom, you need a special certificate to own them. They are often used for controlling pests or hunting deer.

A hollow-point bullet is a specialized type of expanding projectile. Unlike standard bullets, which are often solid, these have a hollow cavity at the tip.

This design is engineered to change shape upon impact with a soft target. By expanding, the bullet transfers more or all of its kinetic energy into the target over a very short distance. This process is known as controlled penetration. It is used to prevent overpenetration, which occurs when a bullet passes entirely through a target. Controlling this is vital in sensitive environments, such as aboard an aircraft, to avoid collateral damage.

The physical mechanism behind this expansion is driven by hydraulic pressure. When the hollow nose strikes a soft medium, material enters the cavity. This creates intense pressure within the pit of the bullet. This pressure forces the internal metal, typically a soft lead alloy, to push outward from the inside. As a result, the axial diameter of the projectile increases significantly.

This phenomenon is commonly called mushrooming because the widened, rounded nose resembles a mushroom sitting on a cylindrical base. The increased frontal surface area creates more drag. This drag limits the depth of penetration while maximizing the energy transferred to the target.

Modern manufacturers use various engineering methods to control how a bullet expands. Some designs feature a jacket—a thin layer of harder metal like copper or brass—that is thinner at the front than the rear. This allows for easy initial expansion followed by a reduced expansion rate. Other bullets use internal partitions in the lead core to stop expansion at a specific point. Some designs even include posts within the hollow cavity to encourage hydraulic expansion.

To prevent the bullet from breaking into pieces, manufacturers may use bonding, which attaches the lead core to the copper jacket. Other types use plastic inserts in the cavity to provide an aerodynamic profile similar to a Spitzer bullet. These plastic tips can also initiate expansion by being forced into the hollow cavity upon impact.

The history of these projectiles is linked to the evolution of gunpowder and metallurgy. In the early days of muzzleloading firearms, soft lead bullets would sometimes deform naturally at high velocities. By the late 19th century, hollowed-out bullets were marketed as "express bullets" to reduce mass and increase velocity. Around 1890, new jacketed hollow-point designs were developed at the British arsenal in Dum Dum, near Calcutta. These included cartridges like the .303" Mk III. While these designs gained popularity among hunters, they were quickly outlawed for use in warfare due to the nature of the wounds they caused.

In the context of international law, hollow-point bullets are subject to significant restrictions. The Hague Convention of 1899, specifically Declaration III, prohibited the use of bullets that easily expand or flatten in the human body during international warfare. This was intended to prevent unnecessary suffering. While some may confuse this with the Geneva Conventions, the Hague prohibition actually predates them. Despite these military bans, hollow-points remain common for civilian and police use. They are valued because they reduce the risk of hitting bystanders through overpenetration. In the United Kingdom, the use of such ammunition is strictly regulated and requires a firearms certificate for specific purposes, such as humane animal control.

Testing the performance of these bullets is a precise science. Experts often use ballistic gelatin to simulate living tissue. They look at three specific metrics to judge success: expanded diameter, penetration depth, and weight retention.

The expanded diameter indicates the size of the wound cavity created. Penetration depth shows whether the bullet can reach vital organs. Weight retention measures how much of the bullet's mass stayed together rather than fragmenting. A fragmented bullet may not penetrate as deeply, which is a factor designers must carefully manage to ensure the bullet performs as intended.

Beyond combat or hunting, hollow-point design plays a role in target shooting. Some specialized bullets incorporate a cavity in the nose called a meplat. This design helps manufacturers maintain a consistent tip shape. A consistent shape leads to more predictable aerodynamic properties among a batch of bullets. While this might slightly decrease the ballistic coefficient and increase wind drift, it allows for much tighter and more consistent shot groupings. This makes the ammunition feel more accurate to the shooter. Additionally, the manufacturing process often creates a flat, uniform base, which provides a consistent surface for expanding gases to push against during firing.