## Ballistic coefficient

The sectional density is not the only factor affecting the retardation (the degree of velocity loss due to the air) of a bullet, as the shape also plays a very large part.

If the form factor i is inserted into the formula, the resulting figure is called the 'ballistic coefficient' of the missile and is the proportion of the bullet's diameter to its weight.

The ballistic coefficient C is calculated by using the formula

where

C = ballistic coefficient; w = weight of bullet; i = form factor; d = diameter of the bullet.

Table 3.3 The ballistic coefficients of various types of ammunition.

Calibre Brand Bullet weight (grains) Bullet type Ballistic coefficient

Table 3.3 The ballistic coefficients of various types of ammunition.

Calibre Brand Bullet weight (grains) Bullet type Ballistic coefficient

 .17 Rem R 25 P-HP Ü.151 .223 Rem R 55 P-SP Ü.2Ü1 .30 Carbine R 110 R-SP Ü.166 .308 Win W 180 S-SP 0.248 .308 Win W 150 P-SP Ü.314 .30-06 F 165 P-BT Ü.47 .38 Spl W 158 R-LD Ü.149 .38 Spl R 158 SWC Ü.146 .357 Mag W 110 F-HP 0.099 .357 Mag F 158 F-SP Ü.145 .44 Mag R 240 SWC Ü.143 .44 Mag F 240 F-HP Ü.172 .45 ACP F 185 F-HP Ü.148 .45 ACP R 230 R-FJ Ü.158

Brand: R Remington, W Winchester, F Federal

Type: P Pointed, S Semi-pointed, R Round nosed, F Flat nosed, SWC Semi-wadcutter, HP Hollow point, SP Soft point, FJ Full jacket, BT Boat tail, LD Lead

Brand: R Remington, W Winchester, F Federal

Type: P Pointed, S Semi-pointed, R Round nosed, F Flat nosed, SWC Semi-wadcutter, HP Hollow point, SP Soft point, FJ Full jacket, BT Boat tail, LD Lead

The form factor is basically a measure of how streamlined a bullet is. For example, a wadcutter bullet will have a form factor of about 2.0, and a sleek, highly streamlined, pointed bullet will have a form factor of 0.55. These figures are published by the various ammunition manufacturers.

Thus, the larger the ballistic coefficient, the better the bullet will retain its velocity and the lower the bullet drop for any given distance.