Bullet Ballistic Coefficient

The Bullet Ballistic Coefficient calculator computes the Ballistic Coefficient a bullet based on the sectional density and form factor of the bullet.

INSTRUCTIONS: Choose units and enter the following:

• (SD) Sectional Density
• (i) Form Factor

Bullet Ballistic Coefficient (BC): The calculator computes the coefficient as a real number.

The Math / Science

A bullet's ballistic coefficient (BC) is a numerical measure that represents its ability to overcome air resistance in flight. It is a crucial factor in determining a bullet's trajectory and performance at longer ranges. The ballistic coefficient takes into account various factors, including the bullet's shape, sectional density, and aerodynamic characteristics.

In simple terms, a higher ballistic coefficient indicates better aerodynamic efficiency, meaning the bullet is more streamlined and experiences less air resistance as it travels through the air. A bullet with a higher BC will typically retain its velocity and energy better over longer distances, resulting in a flatter trajectory and improved downrange accuracy.  This makes a higher ballistic coefficient more attractive.  Based on the equation ballistic coefficient (below), the coefficient increases when the Sectional Density increases or the Form Factor decreases.

Ballistic coefficients are often provided by bullet manufacturers and are used in ballistic calculations to predict how a bullet will behave in different environmental conditions and at varying distances. This information is valuable for shooters and hunters who need to make precise long-range shots.

The formula for a Bullet's Ballistic Coefficient is:

BC = SD / i

where:

• BC = Ballistic Coefficient of a Bullet
• SD = Sectional Density
• i = Form Factor

Bullet Form Factor

Form Factor refers to the shape or design of the bullet. It encompasses various characteristics such as the bullet's overall shape, weight distribution, and features like the nose profile. The graphic shows a sample of Form Factors for various shaped bullets. The form factor can impact the bullet's aerodynamics, stability during flight, and terminal ballistics (behavior upon impact). Different form factors are often associated with specific bullet types, such as full metal jacket, hollow point, or soft point bullets. Manufacturers design bullets with different form factors to achieve specific performance characteristics for various applications, such as target shooting, self-defense, or hunting.

Berger Ammunition list the following for their low form factor bullets:

• 0.925 - 6mm 105 grain Hybrid Target
• 0.925 - 6.5 mm 130 grain VLD Hunting
• 0.915 - 7mm 180 grain Hybrid Target
• 0.891 - .338 300 grain Hybrid OTM Tactical

Caliber

The term "caliber" when referring to firearms and ammunition is a measure of the internal diameter of a gun barrel or the diameter of a bullet. It is usually expressed in inches or millimeters. The diameter of the bullet or the bore of the gun is a critical factor in determining the appropriate ammunition for a particular firearm.

For example, if a firearm has a caliber of .45 inches, it means that the internal diameter of the gun barrel is approximately 0.45 inches. In the context of ammunition, a bullet designed for a .45 caliber firearm would also have a diameter of around 0.45 inches.

It's important to note that caliber is just one aspect of the overall cartridge specification. The complete cartridge information typically includes the caliber, cartridge length, and sometimes additional information, such as the specific type of ammunition or load. Understanding the correct caliber is crucial for selecting the right ammunition for a firearm to ensure proper function and safety.

There are numerous bullet calibers used in firearms, and they vary widely depending on the type of firearm and its intended purpose. Here are some common bullet calibers:

• .22 LR (Long Rifle): Common for rimfire rifles and handguns, often used for plinking and small-game hunting.
• 9mm Parabellum (9mm Luger): Widely used for handguns, including many military and police firearms.
• .45 ACP (Automatic Colt Pistol): Commonly used in handguns, particularly in large-frame pistols.
• .380 ACP (9mm Short): Used in compact and subcompact handguns for self-defense.
• .40 S&W (Smith & Wesson): Popular for law enforcement and self-defense applications, often found in semi-automatic pistols.
• .38 Special: Common in revolvers, used for both self-defense and target shooting.
• .357 Magnum: Similar to .38 Special but more powerful, often used in revolvers.
• .223 Remington / 5.56x45mm NATO: Common rifle cartridges used in civilian and military rifles.
• .308 Winchester / 7.62x51mm NATO: Used in a variety of rifles, including hunting and military rifles.
• 12 gauge and 20 gauge: Common shotgun gauges, used for various applications such as hunting and sport shooting.

These are just a few examples, and there are many other calibers for different firearms and purposes. When selecting ammunition for a firearm, it's crucial to use the correct caliber and type specified by the firearm's manufacturer. Mixing incompatible calibers can be dangerous and may result in malfunctions or accidents.

Firearm Calculators

• Sectional Density: Computes the factor used in the computation of the ballistic coefficient called sectional density.
• Bullet Ballistic Coefficient: Computes factor that represents a bullet's ability to overcome air resistance in flight.
• Ballistic Coefficient from Bullet's Mass, Diameter and Form Factor: Estimates the ballistic coefficient from the mass, diameter and form factor
• Miller Twist Rule: Computes the optimal barrel twist rate for stabilizing a bullet's flight given the bullet's diameter, length and mass.
• Taylor Knock-out Factor: Calculates a factor indicating the power of a round,.
• Greenhill Formula for Optimal Rifling Twist Rate: calculate the optimal barrel twist rate for stabilizing a bullet's flight given the bullet's diameter, length, specific gravity and velocity. 
• Bullet Flight Range: Computes the maximum range (horizontal distance) traveled by a bullet based on the muzzle velocity, elevation angle and shooter height.
• Muzzle Energy of a Projectile: Calculates the kinetic energy in a bullet immediately after leaving the barrel given the bullet's mass and velocity.
• Recoil Velocity of a Gun: Computes the velocity at which a gun will move in the opposite direction in relation to the projectile that it fired.
• Cost per Round: Computes cost per round of ammunition based on the cost of a container of cartridges and the number of rounds in the container.
• Rifle Sight Correction Angles: Computes the Minutes of Angle corrections for rifle sights.
• Shotgun Shell Reloading Cost: Computes the cost to reload used shotgun shells (hulls) with powder, shot, wads and primers.
• Shotgun Shell Loading Cost: Computes the cost to load new pre-primed shells (hulls) with power, shot and wads. 
• Metal Ball Weight: Computes the mass (weight) of a spherical metal (e.g., steel) ball based on the size (diameter).
• Metal Cylinder Weight: Computes the mass (weight) of a metal cylinder based on the size (diameter and length).