The 'ballistic
coefficient' or *bc* is a measure for the drag experienced by a bullet
moving through the atmosphere, which is widely used by manufacturers of
reloading components, mainly in the US. Although, from a modern point of view, *bc*s
are a remainder of the pioneer times of exterior ballistics, ballistic
coefficients have been determined experimentally for so many handgun bullets,
that no treatise on exterior ballistics would be allowed to neglect it..

The bc of a test bullet *bc*^{test
}moving at velocity *v* is a real number and defined as

the deceleration due to drag of a "standard" bullet

devided by

the deceleration due to drag of the test bullet.

The standard bullet is said to
have a mass of 1 lb (0.4536 kg) and a diameter of 1 in (25.4 mm). The drag
coefficients of the standard bullet can be derived from the G1-function given
in literature
and will be named *c*_{Do}^{G1}(*Ma*) .

Using

*c*_{Do}^{test}(*B,Ma*) = *i*_{D}^{test}(*B*) * *c*_{Do}^{G1}(*Ma*)

one finds for the *bc *(assuming
"standard" atmosphere conditions)

*bc*^{test}*=1 / i*_{D}^{test}*(B) * m*_{test}_{ }*/ d*^{2}_{test}

This formula also shows that the *bc*
and the form factor *i*_{D} of a "test" bullet are two
aspects of the same principal simplification: the substitution of the (unknown)
particular drag function of a bullet by the (given) "standard" drag
function of the standard bullet (see also here).