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Discussion Starter #1 (Edited)
Hello everyone, I'm wondering if anyone can help me shed some light on Ballistic Coefficients and how they influence drag curves. I have recently read Brian Litz's book Applied Ballistics for Long-Range Shooting, and I have come to understand what a ballistic coefficient is, how they are derived, and that they are used only when comparing a bullet to a standard bullet such as the G1 or G7. I am confused on how they influence a drag curve. Please correct me if I am wrong on any of the followings points.

-A drag curve is essentially a graph of a projectiles velocity with respect to its coefficient of drag, which helps calculate its negative acceleration due to the effects of the atmosphere at the speed by which it is traveling. The drag curve then is used to calculate the trajectory which determines elevation settings.

- A drag coefficient as it applies to shooting is a number used to quantify the drag or resistance of a bullet as it travels through the air. And because of modern technology like Doppler radar, we wouldn't need a ballistic coefficient because we can find the coefficient of drag as velocity decreases which generates a drag curve. However due to lack of technology and testing capabilities, the use of a ballistic coefficient is used to compare a bullet to a standard bullet.

-A form factor is comparing a bullets (shape) to a standard bullet. It is a ratio of the coefficients of drag. The form factor is also used to scale the standard bullet's drag curve to model the bullet being tested.

-A ballistic coefficient is a combination of sectional density and form factor, which makes sense because you are comparing two shapes and how well they penetrate the air, but you have to factor in the size of the bullet. The BC changes with velocity because the coefficient of drag changes with speed, which changes the form factor, which changes the BC.


My question is and maybe I'm missing something, but if the form factor is used to scale the drag curve of the standard bullet to model the bullet being tested, how does the BC alter the standard's bullet drag curve? Does it scale the curve similar to the form factor?

The image is a picture from Bryan Litz's book Applied Ballistics for Long-Range Shooting, explaining how the form factor is used to scale drag curves.

IMG_1399.JPG
 

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Discussion Starter #2 (Edited)
After further research I have been able to answer my question. I'll post what I have found out if anyone is interested.

We know that

BC = ( SD / i )

i = ( Cp / CG )

SD = M / A


BC = ballistic coefficient
SD = sectional density
i = form factor
Cp = coefficient of drag of bullet tested
CG = coefficient of drag of standard bullet
M = mass of the bullet
A = cross sectional area of the bullet


My question was now that we have the BC, what does the ballistic calculator do with the BC to alter the drag curve? It is as easy as solving the equation for Cp which is the coefficient of drag for your bullet, which is the number needed to generate a drag curve, at each interval in velocity.


Cp = ( CG x SD / BC )


The ballistic computer for each interval in velocity takes the coefficient of drag of the standard bullet and multiplies it by the sectional density of the bullet being tested, and divides it by the ballistic coefficient. This is done many times to form the drag curve, which then goes on to assist in calculating the bullet's trajectory.
 

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Bryan Litz does a seminar twice a year. Check on applied ballistics website. Last I knew, he was doing them in May and November. I attended a November class a year ago in NC and it was great. Bryan made himself available after the seminar for as long as people were asking questions. As part of the class he provided 4 books that he published, one of which had the adjusted ballistic coefficients for many of the bullets out there. This is a big help in you load your own ammo.

Although I don't possess the skill in mathematics as they apply to projectiles, I learned a great deal of practical info. He also spent time dispelling old wives tales. Between lodging meals and class fee it ran just under $1k or so, excluding transportation to/from the facility.

If you want to discuss ballistics at this level, I think BRYAN is your guy.
 
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