"Ask the Rabbi" by R. Mermelstein

What is bullet co-efficient and why is it important in firearm (rifle, pistol or revolver) purchasing consideration ??

Thanks,

Al Lipkin

The ballistic coefficient of any given projectile is a three digit decimal number assigned to it by virtue of its shape and weight. It is an indicator of how well the bullet will retain its initial velocity over any distance. Air is a resistant medium just like water. The heavier and more aerodynamically efficient bullet will have a higher ballistic coefficient. A light .22 caliber bullet of 55 grains, while having a streamlined and pointed configuration, has a B.C. of .235-.243. A 7 mm (.284 diameter) bullet of 162 grains in weight has a B.C. as high as .534. A blunt and cylindrical .357 caliber wadcutter has B.C. of .055. Spire point or Spitzer type rifle bullets will always have a higher B.C. than a round nose bullet of identical caliber and weight. Retention of velocity means retention of striking energy when the bullet reaches its target. However, energy alone is not a figure to be relied upon in choosing a bullet for any given task. Sectional density is another factor in the equation to be considered. S.D. is also a number assigned to a bullet which is an indicator of its penetration properties. It is arrived at by using a bit of simple math: the ratio of the bullet, expressed in pounds (7000 grains equals 1 pound), to the square of its diameter expressed in inches. The higher the sectional density, the deeper the bullet will penetrate. Note that S.D. does not take into consideration the bullet's shape. Note, also, that no consideration is given to the bullet's construction. For the handloader assembling loads for a big game hunt where the game may present itself at the farthest distance a responsible hunter would shoot, both ballistic coefficient and sectional density of a prospective bullet should be studied. Ballistic coefficients of bullets are generally arrived at by using sea level as a benchmark. In theory, the B.C. would be higher as altitude is increased due to the thinner air. Under field conditions, this makes little difference.

Sincerely,

R. Mermelstein