Re: Someone explain BC's to me.. Im Lost
To be precise, let's start with a projectile's drag function. This is the true measure of a projectile's efficiency as it travels through the atmosphere. The DF is merely the projectile's level of drag vs mach number, or velocity. All of your ballistic calculators use drag functions to perform their calculations.
Decades ago, several common projectiles were tested in wind tunnels to develop "standard" drag functions. The projectiles were termed G1,...G7, etc. As you can imagine, testing projectiles was/is an expensive and laborous undertaking. Most of this development also took place before the advent of computers. So...to make ballistic calculations "doable", ballisticians invented the BC. The BC merely relates a projectiles drag function back to a standard projectile's DF. In essence, it is a multiplier on the standard projectile's drag function in order to approximate a drag function for the projectile of concern.
The BC is not an intrinsic measurement of the projectile, or anything for that matter! One can <span style="font-style: italic">infer</span> certain drag performance from it, but I think it important to distinguish that the ballistic coefficient is a derived parameter that relates one projectile to another. Nothing more. And...it was developed so that hand ballistic calculations could be performed in days instead of months.
Another point worth mentioning: one BC does not fit all for a given projectile across its entire drag function or velocity range. In essence, the BC can too vary with velocity. Often you will see several BC's quoted for a projectile, varied with velocity, in order to more accurately predict a projectile's real DF. In the business I was in, we referred to this as "2nd order nonsense", or sometimes, "multiplying reality by bullshit to achieve true understanding."
As you can see, the BC adds a layer of removal and complexity that is no longer required with modern day computing capabilities. This is why I encourage folks with any level of curiousity to move away from BC discussions, and to learn what a drag function is. As a result, you will also become more intimately familiar with how a/your bullet is affected as it travels through its entire velocity range.
My attitude also stems in part from the fact that, historically speaking, bullet manufacturer's have been unable to agree on a standard on how to present and/or measure the data used to derive BC's. This has led to inaccurate representations in the marketplace. Given this, the BC's current and future usefuleness as a comparision basis is dubious, IMHO.
