Glossary of Terms

Glossary of Terms

Posted by Defiant Munitions staff on Nov 26th 2021


Ballistics is the field of mechanics concerned with the launching, flight behavior and impact effects of projectiles, especially ranged weapon munitions such as bullets, unguided bombs, rockets or the like; the science or art of designing and accelerating projectiles so as to achieve a desired performance.

A ballistic body is a free-moving body with momentum which can be subject to forces such as the forces exerted by pressurized gases from a gun barrel or a propelling nozzle, normal force by rifling, and gravity and air drag during flight.


Ballistic Coefficient

In ballistics, the ballistic coefficient (BC, Cb) of a body is a measure of its ability to overcome air resistance in flight.[1] It is inversely proportional to the negative acceleration: a high number indicates a low negative acceleration—the drag on the body is small in proportion to its mass. BC can be expressed with the units kilograms per square meter (kg/m2) or pounds (mass) per square inch (lb/in2)[2] (where 1 lb/in2 corresponds to 703.069581 kg/m2).



In guns, particularly firearms, caliber (or calibre; sometimes abbreviated as "cal") is the specified nominal internal diameter of the gun barrelbore - regardless of how or where the bore is measured and whether the finished bore matches that specification.[1] It is measured in inches or in millimeters.[2] In the United States it is expressed in hundredths of an inch; in Great Britain in thousandths; in Europe and elsewhere in millimeters. For example, a "45 caliber" firearm has a barrel diameter of roughly 0.45 inches (11 mm). Barrel diameters can also be expressed using metric dimensions. For example, a "9 mm pistol" has a barrel diameter of about 9 millimeters. Due to the fact that metric and US customary units do not convert evenly at this scale, metric conversions of caliber measured in decimal inches are typically approximations of the precise specifications in non-metric units, and vice versa.



A cartridge[1][2] or a round is a type of pre-assembled firearm ammunition packaging a projectile (bullet, shot, or slug), a propellant substance (usually either smokeless powder or black powder) and an ignition device (primer) within a metallic, paper, or plastic case that is precisely made to fit within the barrelchamber of a breechloading gun, for the practical purpose of convenient transportation and handling during shooting.[3] Although in popular usage the term "bullet" is often informally used to refer to a complete cartridge, it is correctly used only to refer to the projectile.

Cartridges can be categorized by the type of their primers – a small charge of an impact- or electric-sensitive chemical mixture that is located: at the center of the case head (centerfire); inside the rim (rimfire); inside the walls on the fold of the case base that is shaped like a cup (cupfire, now obsolete); in a sideways projection that is shaped like a pin (pinfire, now obsolete); or a lip (lipfire, now obsolete); or in a small nipple-like bulge at the case base (teat-fire, now obsolete). Only the centerfire and rimfire survived mainstream usage today.


Muzzle Velocity (FPS)

Muzzle velocity is the speed of a projectile (bullet, pellet, slug, ball/shots or shell) with respect to[1] the muzzle at the moment it leaves the end of a gun's barrel (i.e. the muzzle).[2]Firearm muzzle velocities range from approximately 120 m/s (390 ft/s) to 370 m/s (1,200 ft/s) in black powder muskets,[3] to more than 1,200 m/s (3,900 ft/s)[4] in modern rifles with high-velocity cartridges such as the .220 Swift and .204 Ruger, all the way to 1,700 m/s (5,600 ft/s)[5] for tank guns firing kinetic energy penetrator ammunition.


Projectile Weight

Projectile expansion

Monolithic Bullet

Monolithic bullets are bullets which are constructed from a one solid material, usually metal, and do not have multiple components. Unlike jacketed hollow point bullets (JHP), monolithic bullets do not have a jacket, cup, core, or tip. They are instead a solid material, typically copper or a copper-zinc brass alloy, although historically any bullet made of a single type of metal can be referred to as a monolithic bullet.[1] Monolithic bullets depart quite dramatically from the better known lead- or jacketed bullet, and offer a more environmentally friendly alternative to the toxicity associated with lead bullets. As a result of increasing environmental concerns over the toxicity levels found in lead-based bullets, some areas in the United States of America have banned the use of lead bullets for hunting purposes.[2] This increasing awareness of the dangers of lead bullets has led to the development of the modern monolithic bullet, which now provides a viable and accurate alternative to the use of lead for shooting.

Fluid transfer monolithic bullets (FTM) are monolithic bullets which contain a geometry designed to move fluid dense tissue in order to cause wounding to a soft target. Unlike jacketed hollow point bullets (JHP), FTMs do not rely on expansion to function as designed. The geometry of the bullet channels the fluid within a soft target radially away from the bullet's path causing significant trauma and tissue tearing.[9] Because fluid generally has low compressibility it is particularly effective as a cutting tool.[10]

By removing the common failure points associated with a JHP bullet (late/early expansion, failure to expand, jacket separation), FTMs have proven extremely consistent and reliable.[11] Additionally, FTMs are known to be "Barrier Blind", meaning that they do not fail on barriers such as auto glass or sheet metal.[10] The FTM's barrier blind attributes are mostly due to the fact that a monolithic metal bullet (commonly constructed of copper), has greater hardness and lower density than a lead bullet. Therefore, FTMs are able to achieve higher velocity and maintain their structural integrity on contact with barriers, whereas lead core JHPs are traveling at lower velocity and often deform on barriers.


Muzzle Energy

Muzzle energy is the kinetic energy of a bullet as it is expelled from the muzzle of a firearm. Without consideration of factors such as aerodynamics and gravity for the sake of comparison, muzzle energy is used as a rough indication of the destructive potential of a given firearm or cartridge. The heavier the bullet and especially the faster it moves, the higher its muzzle energy and the more damage it will do.


Test Barrel/Twist Rate

In firearms, rifling is machininghelical grooves into the internal (bore) surface of a gun's barrel for the purpose of exerting torque and thus imparting a spin to a projectile around its longitudinal axis during shooting to stabilize the projectile longitudinally by conservation of angular momentum, improving its aerodynamic stability and accuracy over smoothbore designs.

Rifling is often described by its twist rate, which indicates the distance the rifling takes to complete one full revolution, such as "1 turn in 10 inches" (1:10 inches), or "1 turn in 254 mm" (1:254 mm; sometimes expressed as "1:25.4" cm, or something similar. The units are usually easily inferred.) A shorter distance indicates a "faster" twist, meaning that for a given velocity the projectile will be rotating at a higher spin rate.


FBI Criteria/Gelatin Testing

Ballistic Gelatin

Ballistic gelatin is a testing medium designed to simulate the effects of bullet wounds in animal muscle tissue. It was developed and improved by Martin Fackler and others in the field of wound ballistics. It is calibrated to match porcine muscle, which is itself ballistically similar to human muscle tissue.[1][2][3]

Ballistic gelatin is traditionally a solution of gelatin powder in water. Ballistic gelatin closely simulates the density and viscosity of human and animal muscle tissue, and is used as a standardized medium for testing the terminal performance of firearmsammunition. While ballistic gelatin does not model the tensile strength of muscles or the structures of the body such as skin and bones, it works fairly well as an approximation of tissue and provides similar performance for most ballistics testing, however its usefulness as a model for very low velocity projectiles can be limited. Ballistic gelatin is used rather than actual muscle tissue due to the ability to carefully control the properties of the gelatin, which allows consistent and reliable comparison of terminal ballistics.