There’s an old saying, “I carry a handgun, to fight to my rifle.” Rifles are generally considered fight stoppers. They have the best chance of the ever-elusive one-shot stop. Their effects are widely known and when you see one, you know it in an instant. But how do they work? To better understand their affects you need to know more about the rifle projectiles and hydrostatic shock. These two are integral aspects in the study of terminal ballistics—the behavior of a bullet once it impacts a target.
Rifle Projectiles and Hydrostatic Shock
The effect of a projectile on a target, specifically how energy transfer affects living tissue, has implications in hunting, military applications and self-defense. This discussion delves into how rifle projectiles create different effects on targets and the phenomenon of hydrostatic shock or temporary wound cavity, which plays a significant role in the incapacitating effects of high-velocity rifle rounds.
I can remember as a kid, running out in the woods with my friends on hunting trips. We’d get up early to clear the hides of spent casings and every now and then we’d find a live round. I was fascinated by how this bullet could be so devastating. One day, I had finally earned the right to fire a proverbial deer rifle. All I remember is my lip quivering and my shoulder killing me. It would take me decades to fully understand and appreciate their capability.
Rifle projectiles vary greatly in size, shape, and design, each affecting the projectile’s velocity, stability, and performance. Traditional rifle bullets consist of a lead core encased in a copper jacket, although some modern designs use other metals or hollow-point technology for specific applications. The design of the projectile, such as full metal jacket (FMJ), soft point, hollow point or ballistic tip, influences how it interacts with a target and thus the energy transfer.
High-Velocity Projectiles
A crucial factor in how a bullet performs is its velocity. As bullet speed increases, so does its kinetic energy, which directly impacts the amount of energy the bullet can transfer to a target. or in this case, living tissue. High-velocity rifle rounds, such as those fired from an AR-15 and other similar rifles, can reach speeds upwards of 3,000 feet per second. This velocity creates a notable impact and energy transfer, which directly plays a role in the phenomenon of hydrostatic shock. I like to remind everyone there is no such thing as a magic bullet. The destructive nature of rifle rounds is impressive, but all academic if you miss the target.
Hydrostatic shock has the best chance of incapacitating the target when it strikes the vital life processes. These are defined as the body’s ability to produce oxygenated blood, transport oxygenated blood and the central nervous system. That means, the chest or head. As we continue to delve into this subject, do not lose sight of the importance of shot placement.
Secondary Wounding Effect
Hydrostatic shock refers to the secondary wounding effect that occurs when a high-velocity projectile strikes soft tissue, creating a rapid and intense transfer of kinetic energy. The human body and other animals are made up largely of water and soft tissues. Why is this important? Because essentially, they are incompressible or do not change with pressure.
- When a bullet impacts at high speed, it can create a temporary cavity or secondary wound cavity in the tissue surrounding the wound track, displacing tissue radially in all directions or an omni-directional blast wave.
- As the high-speed bullet travels through tissue, it transfers kinetic energy, creating a “shock wave” that rapidly pushes tissue outwards as a result of not being compressible.
- A shock wave can create a cavity in the tissue often several times wider than the bullet diameter itself that stretches and damages tissues and organs not directly touched by the bullet.
- As the tissue recoils and collapses, further injury can occur. This secondary effect is different from the direct mechanical damage caused by the bullet itself, referred to as the permanent wound cavity. This effect has been observed to incapacitate animals and humans even if the bullet does not directly strike vital organs.
How Bullet Performance Impacts Hydrostatic Shock
Not all rifle rounds produce significant hydrostatic shock. The bullet’s speed and energy, along with the density and elasticity of the target tissue, play significant roles. Bullets traveling faster than 2,000 feet per second are generally considered to reach the velocity threshold needed to induce noticeable hydrostatic shock. The bullet’s construction also influences hydrostatic shock. Hollow-point bullets or soft-point bullets are designed to expand upon impact, increasing the area of tissue impacted and potentially increasing energy transfer and the severity of hydrostatic shock.
Conversely, full metal jacket rounds tend to pass through targets with less deformation, creating less hydrostatic shock than expanding bullets. However, we know that when FMJ bullets pass through soft tissue they experience a unique effect, bullet yaw. Because the bullet is slowing down, physics demands that the center of gravity, or the larger part of the bullet, overcomes the smaller part of the bullet. The bullet literally flies through the target sideways until the structural integrity of the bullets compromises and it breaks apart. Depending on the velocity, it can break apart into two pieces or several pieces.
Regardless, these pieces are now secondary missiles traveling radially away from the permanent wound cavity. Because the shock wave is traveling milliseconds behind the physical bullet, the additional damage to surrounding tissue and organs is even more affected. Because their structural integrity is already compromised, they often fail to recoil or collapse back into shape. This additional wounding effect is quite devastating, and combined with the permanent wound cavity, creates impressive outcomes.
Implications for Hunting and Military Situations
Hydrostatic shock’s ability to incapacitate a target quickly has implications in both hunting and military applications.
Hunting. The objective in hunting is often a quick and humane kill. Hydrostatic shock can cause rapid incapacitation, allowing the hunter to ensure the ethical harvesting of game. Hunters often select high-velocity rounds or specialized ammunition to maximize the hydrostatic shock effect.
Military. Hydrostatic shock is important in military situations for evaluating the stopping power of different calibers. A larger, slower round may create a large wound channel but lacks the speed to induce hydrostatic shock. However, intermediate calibers fired at high speeds, such as the 5.56mm NATO used in many military rifles, can cause hydrostatic shock, which is theorized to contribute to immediate incapacitation in combat scenarios.
Another benefit to this hyper-velocity is the ability to penetrate certain types of barriers. Metal barriers display an interesting interaction with this hyper-velocity bullet. As the bullet strikes the metal, the transfer of energy on this hard object is converted into heat. The bullet literally melts the metal, or more accurately, turns it into molten metal. As the shockwave hits the now liquified metal, it craters similar to dropping a pebble into water. The crater created is impressive and oftentimes leads to the complete penetration, depending on the thickness and hardness of the metal. Yet another interesting effect from high velocity projectiles.
Of course, there are varying opinions on this subject. As I’ve mentioned before, if you want to start an argument, mention hydrostatic shock and slowly step back. Some suggest hydrostatic shock is inconsistent or that its effects are overstated. There are variations in individual physiology, the resilience of certain tissues and the unpredictable nature of a bullet’s path through a target, all of which can impact whether or not hydrostatic shock actually occurs. They are not wrong. That’s the hard part to accept. While there are perfect and not so perfect conditions, there are also imperfect conditions to consider. Some argue mechanical disruption (tissue permanently damaged directly along the bullet’s path) is the primary factor in wounding effects rather than hydrostatic shock. Again, they are not wrong.
Shot Placement
Referring back to my earlier statement about this subject, everything is relative to shot placement. If the bullet strikes the vital organs, the permanent wound cavity has the best chance at disrupting or destroying the vital life processes. Under certain conditions, the hydrostatic shock can assist in rapidly incapacitating the target. But those conditions have a lot to do with shot placement. If the shot strikes the vital organs, combined with hydrostatic shock, it has the best chance of immediately incapacitating the target. Regardless of the conditions or opinions, the hard truth is shot placement is still king.
Conclusion
I’m fascinated by the study of rifle projectiles and hydrostatic shock. There is a complex interaction between terminal velocity, bullet design and target physiology as it relates to terminal performance. Hydrostatic shock is a significant, though debated, phenomenon in terminal ballistics that can help explain rapid incapacitation from high-velocity rifle rounds.
While practical applications in hunting and military use emphasize the utility of hydrostatic shock, the variability in its effects means bullet performance and tissue response will continue to be critical areas of research. As advancements in ballistics and ammunition continue, understanding hydrostatic shock and bullet behavior will enhance knowledge in fields ranging from forensics to ethical hunting practices to even self-defense. Exciting times indeed.
