Hi Guys, i've heard that you can work out the true ballistic co-efficient of a bullet from it's measured velocity decay over a given distance, but how does this information translate into a BC? Does anyone have a formula for such calculations or can link me to the information i need? any help would be great

Id suggest two sources. One is Robert L. McCoy's "Modern External Ballistics". Most popular ballistics programs which use BC's are based on the methods described in detail in this book. The math in his work is well proven though not easy reading. The other is the work of Arthur Pejsa. pejsa rifle ballistics software and books His methods don't use the concept of Ballistic Coefficients. Rather it fits coefficients of measured performance to the bullet you're shooting. If you're trying to derive BC's to use for selling bullets to the masses who use software derived from McCoys work then your best bet is to use McCoy's equations (and software) and adjust the G() ballistic coefficient of your choice to give the best fit over your desired velocity range. If you're trying to directly predict trajectories, finding BCs is not a goal in itself, and measuring the characteristics of your bullets from your own shooting tests is is practical for you, then you'll find Pejsa's methods much simpler and typically more accurate.