ballistic coeficient

[BobbleHeadJesus]

whats this all about? tell me all you know!

thanks
lopez

[sneaky beaky]

ta daaaa.... {click h.t.h

and this... {click

[pneuguy]

What is BC?


The ballistic coefficient of the pellet you're shooting helps determine everything from trajectory curvature to wind drift to lethality. BC is therefore a number that's definitely worth knowing.

The instant the pellet leaves the muzzle it starts losing velocity to air drag. Aerodynamics causes this deceleration to occur at a constant rate of percent velocity lost per yard traveled. The rate of velocity loss is inversely proportional to the pellet's BC. Practical BCs for airgun pellets cause rates of velocity loss that run from about 0.35% per yard to 1.3% per yard.

One good way to measure the BC of a pellet (and the method that's used here) is to measure the retained velocity at two different points (one "uprange" near the muzzle, the other farther away "downrange"). The ratio of these two velocities at, and the distance between, the points can then be used to calculate BC -- which can then be used to predict the pellet's velocity ANYWHERE in the trajectory.

The two velocity measurements can be made using two chrono's so that both readings come from the same pellet for any given shot (this is the best way), or with one chrono by walking back and forth for alternating shots.

Steve_in_NC

http://www.airgunexpo.com/calc/calc_bcc.cfm?

Cheers,
Steve