Ballistics is the science and dynamics of projectiles in motion. This multidisciplinary field has helped refine the precision and understanding of various projectiles from bullets to rockets. Ballistics draws its roots from physics, particularly Newtonian mechanics and has been pivotal in the realms of defense and warfare, and also in space research, sports, and many other segments of life.
The study of ballistics is broadly categorized into four distinct segments: internal, transitional, external, and terminal ballistics. Each segment offers insight into a specific phase in the life of a projectile. This is part 2 in our series on ballistics, our earlier article on Terminal Ballistics provides details on how different projectiles behave once they have impacted a target. Let’s get nerdy.Â
Definition of External Ballistics
External ballistics focuses primarily on the trajectory and behavior of a projectile once it has exited the muzzle of the firearm or any launch mechanism, and prior to impact. This is a crucial phase as the projectile interacts with external factors like air, gravity, wind, temperature, etc. which influence its path and eventual point of impact.
The primary concern of external ballistics is understanding and predicting the flight path of projectiles. The trajectory is shaped by many factors, both inherent to the projectile (like its shape, mass, and spin) and external (like air resistance, wind, and gravity). Studying external ballistics provides shooters with the critical information needed to make effective range estimations and adjustments.
The journey of a projectile after leaving the barrel and before impact may seem nearly instantaneous, especially when using firearms with high muzzle velocities; However, the journey is far more complex. Every bullet or missile, regardless of design has to combat air resistance, negotiate crosswinds, and deal with the pull of gravity.
External ballistics bridges the gap between the internal mechanics of a firearm and the terminal impact of a projectile.
Factors Affecting External Ballistics
The behavior of a projectile in flight is a result of numerous intertwined factors. Understanding these allows for greater accuracy and the ability to predict a projectile’s path under various conditions. These factors range from the intrinsic properties of the projectile to external forces acting upon it during its flight.
Initial Velocity
The initial velocity of a bullet is the speed at which it exits the muzzle of a firearm. This velocity is the largest determinant of the bullet’s trajectory, range, and impact energy. A bullet with a higher initial velocity will have a flatter trajectory, allowing it to cover a longer distance before it’s affected significantly by gravity.
The caliber of the projectile plays a direct role in determining its initial velocity. Larger calibers having more mass generally have higher muzzle energies (Sorry 300 Blk fans).
However, they will not necessarily have higher muzzle velocity than smaller calibers. It’s also important to note that while higher calibers may offer more power, they can also be subjected to greater air resistance due to their larger diameters.
Bullet Design & Shape
The design and shape of a bullet play a pivotal role in its flight characteristics. A bullet designed with aerodynamics in mind will encounter less air resistance, maintain its velocity better, and travel further with a more predictable trajectory.
The term “ballistic coefficient” (BC) is used to quantify a bullet’s ability to overcome air resistance during flight. A bullet with a higher BC is more streamlined and will retain its velocity better over long distances. This is why long range shooters often prefer bullets with higher BCs. They offer greater consistency and predictability, especially when dealing with crosswinds. Similarly, this is why heavier 5.56 rounds like the 77gr OTM have become very popular with precision shooters.
Gravity
Gravity is the everpresent force acting on all objects pulling them towards the center of the Earth. For a bullet this means a constant downward force irrespective of its initial velocity or design.
This constant pull results in a phenomenon known as “bullet drop.” As the bullet travels forward it’s continuously being pulled downwards leading to a curved trajectory. The farther the bullet travels the more pronounced this curve becomes leading to a steeper descent towards the ground as velocity decreases.
While all bullets are subjected to gravity, their initial velocity and caliber influences how quickly gravity affects their trajectory. Bullets with a higher initial velocity will cover more ground before gravity can significantly affect their path. Similarly certain calibers due to their weight and design experience different rates of bullet drop over specific distances. Faster and smaller rounds will be less affected while velocity is maintained, but once velocity begins to dwindle experience greater effects.
It’s this intricate dance of forces and bullet characteristics that makes external ballistics a fascinating and vital field for those aiming to achieve shooting precision.
Air Resistance & Drag
A bullet’s journey from the muzzle to the target is not one without resistance. As the projectile travels through the air the primary force acting against it is air resistance, referred to as “drag.”
The force of air resistance acting on a bullet is influenced by a few factors, one of the most crucial being the bullet’s shape and design. Just as aircraft engineers design planes to minimize air resistance, bullet manufacturers pay keen attention to a bullet’s shape to ensure it faces the least amount of resistance while in flight.
This brings us to the term “drag coefficient.” It is a dimensionless number used to quantify an object’s resistance to motion through a fluid, in this case, air. Bullets with lower drag coefficients are more aerodynamically efficient, allowing them to maintain their velocity for longer and face less deviation from their intended path.
Different bullet designs exhibit varying drag coefficients. For instance, boat-tail bullets with a tapered rear end have lower drag coefficients than flat-based bullets, making them better suited for long range shooting.
Wind & Weather Conditions
The atmosphere in which a bullet travels is not static. From gusty side winds to temperature fluctuations, many environmental factors can alter a bullet’s trajectory at different points.
Crosswinds can push a bullet off its intended course, requiring shooters to adjust their aim to compensate. Headwinds and tailwinds are not as influential on the bullet’s lateral movement, but do affect its speed and drop rate.
Moreover, air’s density changes with temperature and humidity. Warmer air is less dense than colder air, leading to less air resistance and better velocity/energy upon impact. Similarly, humidity can slightly affect air density, although its impact on bullet trajectory is generally minimal compared to other factors.
Spin and Gyroscopic Drift
The rifling inside a firearm’s barrel doesn’t just exist for decoration; it serves the essential purpose of imparting spin on a bullet.
This spin stabilizes the bullet, preventing it from tumbling and ensuring it travels in a straight, consistent path. The rifling’s twist rate, which refers to the distance over which the rifling completes one full revolution, is tailored for different bullet grain weights and calibers to provide optimal stabilization.
For example, a bullet that’s stable at 50 yards might begin to show signs of destabilization as it travels further out to 300 or 500 yards. The spin can also lead to gyroscopic drift, a phenomenon where the bullet’s axis of rotation begins to drift, causing the bullet to shift laterally from its expected path, think about a pitcher throwing a curveball.
Comparatively, the lighter and faster 5.56 round stabilizes differently than the heavier .308. At shorter ranges like 50 or 100 yards both may exhibit stable flight. But as they reach out to 500 yards, the differences in their design and mass begin to manifest. The heavier .308 will maintain its stability for longer distances than the 5.56mm.
The stabilization of a 5.56 bullet begins almost immediately upon exiting the barrel due to the spin imparted on it by the rifling of the barrel. The rifling is designed to give the bullet a gyroscopic spin, which stabilizes the bullet and prevents it from tumbling in flight. This stabilization ensures the bullet follows a more predictable trajectory.
The question about when the 5.56 bullet “begins to stabilize” might be rooted in a common misunderstanding. Bullets don’t leave the barrel in an unstable state and then stabilize in mid-air. Instead, they are stabilized by the spin from the moment they leave the barrel.
However, what can happen is that bullets if not matched properly to the rifling twist rate, can yaw or “wobble” slightly in flight. This yaw is most pronounced immediately after the bullet exits the muzzle and gradually diminishes as the bullet moves downrange, until about 500 yards. This phenomenon is sometimes referred to as “going to sleep.” So, when people talk about a bullet “beginning to stabilize,” they might be referring to this yaw diminishing and the bullet flying more perfectly nose-forward.
For the 5.56mm round, the commonly used rifling twist rates are 1:7 for 62gr and heavier rounds, 1:8 for 50-70 gr bullets, and 1:9 for 62gr and less rounds. The ideal twist rate varies based on the specific weight and design of the bullet. Matching the right bullet weight to the appropriate twist rate is what creates stabilization and accuracy.
 Gyroscopic Drift
Gyroscopic drift is also intricately tied to the Coriolis effect, a result of Earth’s rotation. Unless you shoot long range, and I mean looongggg range, this likely will not effect you.
For those crazy long shots, shooters might need to account for this effect, especially in the East-West direction, as the bullet can be influenced by the Earth’s movement during its time in flight.Â
Trajectory Analysis
Understanding the trajectory of a projectile is one of the largest contributors to precise shooting. This section delves deep into certain aspects of bullet trajectory, clarifying concepts and stressing the importance of factors like maximum ordinate, point blank range, and the significance of zeroing.
Definition of Maximum Ordinate and Point Blank Range
The bullet’s path from the barrel to the target is not a straight line. Due to gravity and other factors, the bullet follows a curved path. This leads us to two crucial concepts in external ballistics.
Maximum Ordinate: This represents the peak of the bullet’s curved trajectory—the highest point the bullet reaches above the line of sight. When a bullet is fired, it first rises above the line of sight, achieves the maximum ordinate, and then starts descending towards the target.
Point Blank Range: This is a term that confuses many but is important for hunters and tactical shooters. Point-blank range refers to the distance at which a shooter can aim directly at the target without having to adjust for bullet rise or drop. It means that within this range, the bullet’s trajectory will not deviate from the target’s size, allowing for a direct aim and hit. A little different than what we all thought it meant, but in terms of shooting this is the proper definition.Â
Zeroing and Its Importance
Having your firearm “zeroed” is the foundation of accurate shooting. But what does it mean?
Zeroing: It is the adjustment of firearm sights so that the point of aim (where you’re aiming) aligns perfectly with the point of impact (where the bullet hits) at a specified distance. When a shooter says their rifle is “zeroed at 200 yards,” they mean that if they aim at a target 200 yards away, the bullet will hit where they aimed.
Proper zeroing is essential for various reasons. For one, it provides the shooter with a predictable starting point. If the firearm is zeroed at a known distance, the shooter can make educated adjustments for targets closer or farther away than the zeroed distance. Secondly, in tactical or hunting scenarios, being off by even an inch can mean missing the target altogether. Thus, having a weapon system accurately zeroed can be the difference between success and failure.
The trajectory of a 5.56mm round will vary based on multiple factors including bullet weight, bullet shape (ballistic coefficient), muzzle velocity, and atmospheric conditions. However, one common 5.56mm round is the M855 with a 62-grain weight. Using this as a general example and assuming standard atmospheric conditions and a typical muzzle velocity.
5.56mm M855 Bullet Trajectory when Zeroed at 50 Yards:
- 50 Yards: The bullet impacts where the sights are aimed, as this is the distance at which the rifle is zeroed.
- 100 Yards: Due to the bullet’s upward trajectory after exiting the muzzle (as it intersects the line of sight twice), the bullet will usually impact slightly high at 100 yards, often between 1.5 to 2.5 inches above the point of aim.
- 200 Yards: The bullet starts its descent but might still impact slightly above or around the point of aim depending on various factors like the barrel length. It might be around 0-2 inches high, or it may be closer to point of aim depending on specific bullet characteristics and firing conditions. You’re more likely to see a higher impact out of a 20+ inch barrel.
- 500 Yards: By this distance, the bullet has dropped significantly below the line of sight, possibly 50 inches or more (roughly 4 feet or more) depending on specific conditions.
It’s important to remember these are general estimations and can vary based on specific ammunition characteristics, rifle barrel length, and atmospheric conditions.
Modern Tools & Technologies
The world of ballistics is ever-involving, allowing for newer technology to segment traditional principles of marksmanship.
These contemporary innovations enable shooters, researchers, and enthusiasts to attain a deeper understanding of external ballistics, ultimately refining accuracy and predictability.Â
Ballistic Calculators
A ballistic calculator is seamlessly integrates complex mathematical formulas and real-time environmental conditions to offer precise shooting solutions. There are many free ones online that can help you once you put in information such as velocity, barrel length, round characters, and environmental information.Â
Functionality: At its core, a ballistic calculator predicts how a bullet will travel under a given set of conditions. By inputting data like muzzle velocity, bullet weight, ballistic coefficient, altitude, and wind conditions, shooters can receive accurate adjustments for their rifle scope. This takes some of the guesswork out of long-range shooting.
Radar & Doppler Systems
Beyond the traditional tools, radar and Doppler systems represent the pinnacle of ballistic data gathering. These systems offer real-time insights into the flight behavior of projectiles, a feat unachievable just a few decades ago.
Functionality: Using high-frequency waves, these systems track the projectile throughout its flight, recording data on velocity, spin, and trajectory. This wealth of data can be used to validate the predictions of ballistic calculators and refine bullet designs.
Use Cases: While the common shooter might not have access to these advanced systems, ammunition manufacturers and research institutions utilize them extensively. They aid in the research and development phase, allowing for the design of more aerodynamic and efficient bullets. Additionally, defense sectors employ these systems to fine-tune artillery and missile launches.
The integration of these modern tools with time-tested shooting techniques has led to a new era in ballistics. As technology continues its march forward, we can only anticipate even more refined and accurate tools for the external ballistics community.
Practical Applications & Importance
Understanding external ballistics isn’t just a theoretical pursuit or a topic reserved for armchair experts. its real-world applications span across various domains, profoundly impacting the accuracy, safety, and success in each of them. From the rigorous demands of the military to the precision needed in sports shooting and the ethical considerations in hunting, grasping the principles of external ballistics becomes a critical skill. This section delves deep into its vital significance across diverse fields.
Military & Law EnforcementÂ
The battlefield and tactical operations are where minimizing error becomes very important.
Precision shooting and sniping: For snipers and sharpshooters understanding the bullet’s trajectory, wind adjustments, and other external factors is 90% of the job.
Artillery: The role of external ballistics isn’t limited to small arms. When dealing with artillery, predicting the projectile’s path is critical. Here factors like air resistance, gravity, and spin greatly influence where shells or missiles land.
Sport & Competitive ShootingÂ
The world of competitive shooting hinges on accuracy and consistency. Here the slightest miscalculations can be the difference between victory and defeat.
Improving Accuracy: Competitive shooters invest significant time in understanding external ballistics. By grasping how different factors influence a bullet’s flight, they can make informed decisions on ammunition selection, sighting, and shooting technique.
Hunting: Hunting combines skill and ethical responsibility. For a hunter, it’s not just about hitting the target, but ensuring it’s done humanely.
Ethical Shots: Understanding bullet trajectory helps hunters place shots effectively, leading to quick and humane kills. This minimizes the chances of wounding and prolonging an animal’s suffering.
Safety Considerations: Being aware of a bullet’s arc and potential flight path also underscores safety. It ensures that hunters remain aware of what lies beyond their target, reducing the risk of unintended harm. Remember Otis from The Walking Dead?
Trap shooting and bird/waterfowl hunting
External ballistics applies to any moving projectile, including shotguns. This becomes very important for hunting birds and trap shooting. A shooter in these situations must know the spread of the weapon to be effective, which is defined by both barrel length and load characteristics. Shotgun loads behave differently, and that is why we don’t use home defense shotguns for hunting and vice-versa.
The principles of external ballistics find their application in diverse fields, emphasizing its foundational importance. Whether it’s for professional, sporting, or recreational purposes, understanding the science behind a projectile’s flight is key to achieving desired outcomes.
Final Thoughts
From the moment a bullet exits the barrel to the point it meets its target the journey it undergoes is influenced by a myriad of factors – this intricate dance is governed by the principles of external ballistics. As we’ve navigated through its facets, from the foundational physics to its real-world application across disciplines, the significance of external ballistics is clear to see.
Understanding external ballistics is key to better shooting accuracy, making informed decisions in real-time scenarios, and ensuring safety. The advent of modern tools and technologies allows shooters to be better equipped than ever to understand and predict the behavior of projectiles in flight.
For those interested in continuing their education in external ballistics, the book “Modern Exterior Ballistics by Bob McCoy is a very comprehensive review of the topic.
