Calculating Ballistic Coefficient, need smart people help

[hadmanysons]

I'm trying to calculate ballistic coefficients using different drag functions and bullet types but I guess I don't understand it well enough. I'm using the formula

BC = ((Bullet weight in grains)/7000) / (diameter in inches squared), then divide that by (bullet's drag coefficient/Drag Function).


My question is, how do I find out what the drag coefficient of a bullet is. I know the formula but what i'm looking for is a table or a place that already knows those figures. For example, that a Spitzer Boat Tail has a drag coefficient of .295 or something.

Also, I don't really understand what the Drag Function is. I've done lots of googling but I can't what i've read to the formula. I just don't understand it well enough.

Any help will be happily accepted.

 

[Lucky]

Seems to change with velocity too. BC=FormFactorxSectionalDensity.

 

[JohnKSa]

Most bullet manufacturers will provide you with that information for their products.

 

[benEzra]

The ballistic coefficient depends on the individual bullet, i.e. not all spitzer boattails will have the same BC. Best bet is to go the bullet manufacturer's website and look up the ballistic coefficient. For example, the BC of a .311 Wolf 122gr JHP bullet (7.62x39mm) is 0.257, and that of a .311 Wolf 148gr FMJ used in their 7.62x54R ammunition is 0.478.

 

[hadmanysons]

I know they are not all the same, I just couldn't find a place to get that information. My problem has been determining Form Factor.

 

[Lucky]

The PDF is Sierra BC's from their website. Not entirely clear what makes a bullet more slippery, but being the opposite of blunt.

http://www.shootingsoftware.com/coefficients.htm
http://accurateshooter.wordpress.com/2007/07/10/283/

 

[snipe300]

Try looking on www.snipershide.com/forum They might be able to help you if no one here can.

 

[Zak Smith]

Find a copy of McCoy's Modern Exterior Ballistics

 

[patrick526]

I think there's something wrong in your formula. It's not "diameter in inches squared", but "diameter squared".

For more info about BC, look here: http://www.shootingsoftware.com/coefficients.htm

 

[hadmanysons]

I think there's something wrong in your formula. It's not "diameter in inches squared", but "diameter squared".

Well... It is diameter squared, where diameter is inches. I struggled with how to convert the formula to engrish.

Thanks for the links and files and info. I'll look into it all.

 

[hadmanysons]

Find a copy of McCoy's Modern Exterior Ballistics

This book is $60, USED! I might just borrow a copy

 

[Zak Smith]

It's worth it.

 

[Flyboy]

Drag coefficient is a really long and drawn-out topic, and it depends on the shape of the projectile. It can be determined mathematically, but that gets into all sorts of ugly equations and computational fluid dynamics. I've worked in that supercomputer lab (I was an intern, but still), and trust me when I tell you that you really don't want to go down that road. (Incidentally, I'm also a flight instructor; I have at least a rudimentary knowledge of aerodynamics.)

Drag coefficient should be available from the bullet manufacturer. Ballistic coefficient is almost always published. If BC isn't given, any decent manufacturer will provide it if you call them, or at least provide the drag coefficient so you can calculate it.

 

[Ridgerunner665]

It's worth it.

Every penny...

 

[hadmanysons]

Ballistic coefficient is almost always published. If BC isn't given, any decent manufacturer will provide it if you call them, or at least provide the drag coefficient so you can calculate it.

Yeah. I looked up the formulas for drag coefficient and my head started hurting.... more. I'm just looking for a rudimentary way to calculate it based on those factors. I already know how to do it based on the two velocity method.

 

[Ridgerunner665]

To accurately figure drag coefficient, you'd need access to a wind tunnel.

 

[JohnKSa]

Yup, there's a reason wind tunnels are still in use. It's not because companies can't hire smart people to do math for them and write computer programs.

 

[hadmanysons]

I guess i'll just have to rely on the manufacturer.