Ballistic Coefficient of.....

[mark mcj]

I'm trying to make a bullet drop chart for my AR. I'm shooting Swiss 62 gr. 5.56 ammo. It's the GP90 Ammo. I know there a lot of really smart guys out there, what's the formula?
OAL lenght x weight divided by the circumference?

 

[E357]

I thought the way to "compute" the BC of a projectile was to shoot the the projectile between two chronographs a known distance apart and measure the drop in velocity. Once you have the BC then you can figure out all sorts of neat things.

Your formula seems to relate to sectional density which is related to but not the same as BC.

Elliot

 

[HSMITH]

Elliot has the right answer for figuring the ACTUAL BC. You should be able to get somewhat close though by shoooting at 100, 200, 300, and hopefully further, then you can backfigure the BC using drop and muzzle velocity. Do a search on the net for "ballistics calculators" and see what that shows you.

 

[yzguy]

here ya go:
http://www.eskimo.com/~jbm/ballistics/bcv/bcv.html

but I guess you would need need 2 chrono's...

 

[mark mcj]

I guess I'm off to the range.

 

[LewG]

Try this site for good BC estimator, jacketed and cast bullets. - Lew

http://www.uslink.net/~tom1/calcbc/calcbc.htm

 

[mark mcj]

If anyone else is interested, with the BC calculator I came up with .239.
When shooting over a chronograph, first at 15 feet then moving the chrono out to 100 yards, the BC came out to .244.
This is for Swiss 62 grain GP90.