Ballistics is one of the most interesting areas in the field of firearms to me. The broad study of ballistics is divided into several subcategories, studying every step the bullet goes through from before it is fired to after it hits the target, and everything in between. Today we are going to discuss terminal ballistics, a subcategory concerned with the behavior and effects of a projectile as it makes contact with its target. The study of terminal ballistics has been instrumental in the development of better defensive ammunition, military weapons, ammo selection, and law enforcement duty weapon selection. Let’s get a little nerdy and have some fun.

Defining Terminal Ballistics

Ballistics is the science of projectiles in motion which is comprised of four distinct branches, internal, transitional, external, and terminal ballistics.

Internal ballistics concerns itself with the projectile’s behavior inside the firearm before exit. Transitional/intermediate focuses on the projectile from the time it leaves the muzzle until the pressures behind the round stabilize.

External ballistics studies the bullet’s path through the air, including rises, falls, and stabilization/destabilization.

Terminal ballistics examines the projectile’s behavior and affect upon impacting the target.

In the context of firearms, terminal ballistics investigates the performance of bullets upon striking a target. This study is crucial for understanding the effectiveness of different bullets in various situations, such as hunting, self defense, and for optimizing bullet design to achieve specific outcomes.

Factors Influencing Terminal Ballistics

Various factors influence a bullet’s performance upon impact with a target. Some of the most significant factors include bullet design, velocity, and target material.

Bullet Design

The construction and shape of a bullet dramatically affect its terminal performance.

Full Metal Jacket (FMJ) bullets feature a soft lead core encased in a harder metal like copper. FMJ bullets are designed to maintain their shape upon impact, which can result in over penetration and limited damage to the target.

Over penetration is a greater risk with rifle rounds, especially larger calibers that are less likely to fragment upon impacting the target. Conversely, the M193 5.56 FMJ travels at speeds exceeding 3,200 FPS, and often yaws and fragments upon impacting a target due it’s speed and design. This leads to devastating damage in soft tissue.

FMJ pistol ammunition, 9mm for example, generally passes through the target creating a minimal permanent wound cavity due to its lower velocity.

Hollow Point bullets have a hollow cavity in the tip, designed to expand upon impact. Hollow points have been around for decades and are continually improving dramatically based on the study of terminal ballistics.

Hollow point bullet expansion
Federal HST 230gr 45 ACP expansion in soft target

In past decades some hollow points used metal designed to expand dramatically but was too soft and would not penetrate heavy clothing. Other hollow points were made too rigid and would not expand at all unless striking hard objects.

Further, others would get clogged by clothing and not open. All of these problems have been rigorously studied and the free market answered with innovative designs to eliminate these problems. For example, Hornady critical duty has a rubber plug in the hollow point designed to encourage expansion and prevent clogging.

I know the 45 ACP won two world wars, but like stated above, FMJ pistol rounds poke holes in the target and transfer less energy because they tend to penetrate through. This is why hollow points, even a 38 hollow point for example, will likely cause greater damage overall.

The hollow point serves two primary purposes in the context of terminal ballistics.

The first is to expand, creating a greater surface area and a larger wound channel. The second is to expand and dump all the kinetic energy the bullet is carrying into the target it slows.

You know on the back of ammo boxes where it says the velocity and energy of the round? Energy is measured foot-pounds, this was often referred to as the “Stopping power” of a round. We may dig into they myths and misconceptions of stopping power in a later post, however stopping power has been researched and is still somewhat of a contentious theory.

That said, the energy produced by a round is an important measurement. When it comes to hollow points, as they expand and stop inside a target, they transfer that kinetic energy into the target as they are stopped. This is one of the reasons hollow points are more affective at transferring energy than FMJ rounds, which often penetrate clean through. The expansion increases the bullet’s diameter, creating a larger wound channel and greater energy transfer, while reducing the chance of over penetration.

Soft point bullets have an exposed lead core without a jacket. This is typical of older revolver ammunition, but can still be found today. Soft point projectiles deform when they impact hard targets, more slowly and less controlled than hollow points. They are less likely to over penetrate than FMJ rounds.


A bullet’s velocity at impact significantly affects its terminal performance. Higher velocities generally result in more significant energy transfer and greater damage to the target. However, velocity can also impact a bullet’s stability and accuracy, making it important to know the effective barrel length and distance for the specific round.

To illustrate this, we will use the M855 5.56 round, formerly the standard issue round of the U.S. military. In the mid 2000s the U.S. Army began a study to find a more effective CQB round based on anecdotal reports from soldiers.

What they found was that at close range the M855 was still superior to the 7.62×51 when it yawed. Yawing is when a bullet impacts the target at an angle, becomes unstable, and fragments inside the target. The M855 was absolutely devastating when it yawed upon entering a target. Yaw is created by velocity and destabilization, from a 16 inch barrel that is typically the first 0-150 yards (external ballistics) and past 500 yards with M855. However, this was during the popularity of the Mk18, a 10.5 inch barreled AR, which lowered the velocity (internal ballistics) of the round, reducing yaw.

The U.S. Army ended up adopting the M855A1, which improved on the M855 cartridge.

Target Material

The composition and density of the target material influence how a bullet behaves upon impact.

For example, bullets impacting soft tissue will behave differently than those striking harder materials like bone or steel. Ballistic gelatin is commonly used in testing to simulate human tissue, providing valuable information on bullet performance. Keep in mind, it’s designed to simulate, and is nowhere near an exact analogue.

Further, soft point bullets tend to be easily deformed and stopped by stronger objects. Some hollow will yaw and not expand when they impact plywood. Similarly, M855 and other “Barrier blind” rounds are made to defeat cover such as car doors, walls etc. They are not perfect, and will deform, yaw, etc, but will still remain mostly intact when impacting a target behind the barrier, creating devastating results.

Final Thoughts

Terminal ballistics is a vital aspect of understanding a bullet’s effectiveness upon impacting a target, even steel body armor. By considering factors such as bullet design, velocity, and target material, experts can optimize bullet performance by creating specialized rounds for various applications. Hopefully this understanding will help you make informed decisions about the most suitable ammunition for your purposes.

Due to modern terminal ballistic studies we have bullet designs and models that vastly outperform either larger or faster rounds. Take the 147gr Federal HST 9mm at 1,000 FPS for example. This round is widely used by law enforcement because the weight and lowered velocity combined with the bullets design will expand rapidly, dump its energy, and reduce the risk of over penetration. Law enforcement is especially concerned about (lawsuits) over penetration in urban settings where someone could be injured by an errant shot through a wall.

From law enforcement to hunters and recreational shooters, understanding terminal ballistics is key to achieving the desired outcome with every shot.

The opinions expressed in this post are those of the author and do not necessarily reflect the views and opinions of Tacticon Armament.