What is a good ballistic coefficient?

On the G1 scale, streamlined rifle bullets typically have a B.C. of about 0.2 to 0.7 lb/in2. The higher this value is, the better for long range shooting. Values for handgun and round ball ammunition are much lower, usually below 0.2. What is considered "good" depends on the intended use. For short range hunting bullets a high B.C., as required by target rifle ammo for long range shooting, is not necessary.

How to calculate ballistic coefficient?

You divide the sectional density by a form factor. The sectional density is the value obtained when you divide the weight of the projectile by the square of its diameter. When given in grains and inches, first divide the weight by 7000 then divide that by the square of the diameter. The form factor is determined from the shape of the projectile relative to standard models (G1 or G7). Manufacturers usually list the form factor or publish the ballistic coefficient (BC) directly.

What are the differences between G1 and G7 ballistic coefficients?

These use different standard bullet shapes. The G1 shape is a flat based and round nose reference shape that is most commonly used as the reference for manufacturer specified BCs. The G7 shape has an elongated boat tail shape which fits modern low drag bullets better. As the value of G1 will be higher than G7 for the same bullet, only BC values measured using the same model can be compared.

Is the ballistic coefficient constant at all speeds?

It is not completely constant. The stated BC is a practical average but the actual drag changes as the projectile crosses the transonic region and becomes less efficient. According to Doppler radar single projectile BC values change by several percent during flight. For this reason accurate long range ballistics tables use BC values that are broken down into speed ranges.

Is cross-sectional density equal to ballistic coefficient?

There are differences. The cross-sectional density is determined only by weight and diameter, while the ballistic coefficient also takes into account the shape of the projectile through the form factor. Cross-sectional density is a starting point, and aerodynamic shape of the tip is key to converting high cross-sectional density into a high ballistic coefficient.

Ballistic Coefficient Calculator

Projectile details

Calculation model

Form factor (G1 / G7)

Drag coefficient (Cd)

Bullet weight

Bullet diameter (caliber)

Form factor (i)

Ballistic coefficient (lb/in2)

Enter the bullet weight and diameter to compute its ballistic coefficient.

Please input values into the fields

Reading your result

A higher ballistic coefficient means the projectile slows less in flight: a flatter trajectory, less wind drift, and more energy kept downrange.

The ballistic coefficient (BC) is a value that indicates the ability of a bullet to maintain its velocity while traveling through the air. Bullets with a high BC cut through the air more easily and lose speed more slowly.

Balls with a low BC are slowed down by air resistance more than those with a higher BC. This difference determines how far the ball will go, how much it is deflected by the wind and what energy it has when it hits its target.

What is Ballistic Coefficient?

Air resistance increases the larger the frontal area of a bullet is and decreases with more weight behind the frontal area. The ballistic coefficient combines this relationship. The heavier a bullet is relative to its diameter and the smoother its shape, the higher its BC.

The same physics applies to more than just shooting ranges. High-BC reentry capsules can maintain their speed at high altitudes while lighter reentry capsules will lose velocity early and reach subsonic speeds.

Formula for ballistic coefficient.

For small projectiles, ballistic coefficient is a value that divides sectional density by a form factor.

\text{BC} = \frac{\text{SD}}{i}

The sectional density is a value that divides the weight by the square of the diameter and the form factor represents the shape. For shooters using grains and inches, the sectional density is expressed with this formula:

\text{SD} = \frac{W_{\text{grains}}}{7000 \times d_{\text{inch}}^{2}}

7000 is used to convert grains into pounds. So both the unit of sectional density and ballistic coefficient are in pounds per square inch. For example, consider a bullet with 168 grains, a diameter of .308 inches, and a form factor of 1.12.

\text{SD} = \frac{168}{7000 \times 0.308^{2}} = 0.253 \ \text{lb/in}^2

\text{BC} = \frac{0.253}{1.12} = 0.226 \ \text{lb/in}^2

The table below shows each symbol in this example and its corresponding numeric value.

Symbol	Meaning	Example
W	Bullet weight (grains)	168
d	Bullet diameter (inches)	0.308
SD	Sectional density (lb/in2)	0.253
i	Form factor (shape)	1.12
BC	Ballistic coefficient (lb/in2)	0.226

Let's just look at cross-sectional density.

The cross-sectional density alone is worth analyzing. Before the shape is considered, it is determined by weight and diameter alone and represents an upper limit. An excellent bullet shape aims to approach this upper limit.

For the same caliber, heavier bullets always have a higher sectional density. Therefore longer and heavier bullets tend to have a higher ballistic coefficient relative to their calibers.

Form factor and resistance models for G1 or G7.

The shape factor compares the drag of a ball to that of a standard body. A value close to 1 indicates performance similar to a standard body; a value below 1 means less drag while a value above 1 indicates that the shape is more blunt.

There are several reference shapes. The G1 model is based on a flat, short and blunt bullet tip and is the most commonly used reference value as published by manufacturers. The G7 model instead uses an elongated boat tail shape as its reference which makes it better suited to modern streamlined bullets. So a particular bullet may have a higher BC in the G1 system than in the G7 system even though the apparent value is lower in the G7 system.

Model	Standard shape	Best for
G1	Flat base, blunt 2-caliber nose	Most factory-quoted BCs
G7	Long 7.5 degree boat-tail	Modern very-low-drag bullets
G5	Short boat-tail	Moderate boat-tail bullets

Resistance coefficient model.

Engineers and physicists often use a different definition based on measured resistance values rather than form factor.

C_b = \frac{m}{C_d \times A}, \qquad A = \frac{\pi d^{2}}{4}

Here the unit for mass is kilograms, the unit for projected area is square meters and the unit for result is kg/m2. This is a valid ballistic coefficient but it represents a different quantity than G1 or G7 values so they should not be directly compared. In the calculation tools this model is offered as a standalone mode.

Typical values for ballistic coefficient:

The figures below are rough g1 values and serve to give a general idea. The actual values depend on the type of ammunition and its speed.

Projectile	Approximate G1 BC (lb/in2)
Lead round ball	0.02 to 0.07
Handgun bullet	0.10 to 0.20
Typical hunting rifle bullet	0.30 to 0.50
Long-range match bullet	0.50 to 0.70
Heavy .50 BMG match bullet	0.90 to 1.10

Does ballistic coefficient change with velocity?

In reality it changes. Published BC values are usually considered to be approximately constant within a given speed range but as the bullet slows from supersonic to subsonic speeds the actual drag on the bullet is changing.

Measurements with Doppler radar have shown that the BC of a single bullet can vary by several percent during flight. For this reason, serious manufacturers often give an average BC over a range of velocities or publish multiple BCs for different velocity ranges rather than just one precise number.

Why the ballistic coefficient (BC) affects trajectory:

Even if a bullet leaves the barrel at exactly the same speed, it can strike in a different place far down range. Bullets with higher B.C.'s have more retained velocity, less drop and less wind drift. This is why shooters often strive to increase their B.C. by even one hundredth of a point.

The Ballistic Coefficient is a model and not a law of nature. Consider the results presented here to be reliable estimates. Compare these values with those published by the manufacturer or your own measurements using a chronograph before adjusting your scope for long range shooting.

This calculation tool is for educational purposes and planning of ammunition choices. Make sure to follow safe handling procedures for firearms and the laws that apply at your shooting range.

Frequently asked questions

What is a good ballistic coefficient?: On the G1 scale, streamlined rifle bullets typically have a B.C. of about 0.2 to 0.7 lb/in2. The higher this value is, the better for long range shooting. Values for handgun and round ball ammunition are much lower, usually below 0.2. What is considered "good" depends on the intended use. For short range hunting bullets a high B.C., as required by target rifle ammo for long range shooting, is not necessary.
How to calculate ballistic coefficient?: You divide the sectional density by a form factor. The sectional density is the value obtained when you divide the weight of the projectile by the square of its diameter. When given in grains and inches, first divide the weight by 7000 then divide that by the square of the diameter. The form factor is determined from the shape of the projectile relative to standard models (G1 or G7). Manufacturers usually list the form factor or publish the ballistic coefficient (BC) directly.
What are the differences between G1 and G7 ballistic coefficients?: These use different standard bullet shapes. The G1 shape is a flat based and round nose reference shape that is most commonly used as the reference for manufacturer specified BCs. The G7 shape has an elongated boat tail shape which fits modern low drag bullets better. As the value of G1 will be higher than G7 for the same bullet, only BC values measured using the same model can be compared.
Is the ballistic coefficient constant at all speeds?: It is not completely constant. The stated BC is a practical average but the actual drag changes as the projectile crosses the transonic region and becomes less efficient. According to Doppler radar single projectile BC values change by several percent during flight. For this reason accurate long range ballistics tables use BC values that are broken down into speed ranges.
Is cross-sectional density equal to ballistic coefficient?: There are differences. The cross-sectional density is determined only by weight and diameter, while the ballistic coefficient also takes into account the shape of the projectile through the form factor. Cross-sectional density is a starting point, and aerodynamic shape of the tip is key to converting high cross-sectional density into a high ballistic coefficient.

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Disclaimer: This calculator is provided for general informational and educational purposes only. Our calculators are under active development, and results may be inaccurate, incomplete, or unsuitable for your situation. Always verify the figures independently and seek advice from a qualified professional before relying on them. We make no warranties and accept no liability for any loss or decision arising from use of this tool.

References

Ballistic coefficient — Wikipedia
Overview of the small-arms and physics definitions, the G drag models, and the history.
Sectional density — Wikipedia
Definition of sectional density and its role in penetration and BC.
Courtney M, Courtney A. The Truth About Ballistic Coefficients (2007)
Peer-style analysis of how measured BCs compare with advertised values.
Litz B. Applied Ballistics for Long Range Shooting (2nd ed., 2011)
Standard reference on form factors and G1 vs G7 ballistic coefficients.
Nennstiel R. How Do Bullets Fly? — Ballistic coefficient
Educational exterior-ballistics reference on drag and the ballistic coefficient.