How do you figure the BC?

mountaineer magic · 03-16-2009, 07:46 AM

I have a question. I can't remember how to figure the ballistic co-efficient of a bullet. I wanted to do some trajectories but the program I have wants the BC not just the weight, cal., and MV.
Can anybody help me with the formula. The bullet is a .451 sized to .448, it is 530 grain. thanks

Underclocked · 03-16-2009, 08:21 AM

http://www.loadammo.com/Topics/September01.htm

http://www.eskimo.com/~jbm/cgi-bin/jbmbcv-5.0.cgi

I do NOT concern myself with BC. It's not only somewhat arbitrary, it changes with range. Only useful as a gross indicator, IMHO.

Semisane · 03-16-2009, 08:58 AM

On the upper left side of this page is a simple BC calculator that it probably "good enough" for most purposes. All you need to do is enter in the diameter, weight, and shape.

http://www.handloads.com/calc/

mountaineer magic · 03-16-2009, 11:45 AM

Thank you guys . I don't take much stock in the BC but the program requires it in order for me to figure some trajectories. I wanted to try some long range target shooting and thought the trajectory info would help me to get started. I went to the hardware store and they had a mic. soi got the exact sizes.the bullet is .448 base diam.,length is 1.423 in.,nose length is .638,tip dia. is .180, and weight is 538 gr. sec. density is .368. So I will look up the links and see if I can get this figured out
thanks UC and Semi

spaniel · 03-16-2009, 12:23 PM

Stick in 0.2 for the BC of a ML bullet and that will get you close enough to get on a target at 200 yds, and adjust from there.

Published BCs for ML bullets are horribly inflated from what I find them to be when I shoot them. For some reason they are much more honest with centerfire bullets.

What I usually do is shoot the gun and determine the real-life drop at 100 and 200 yards, get the velocity off my chrono, then put it in the calculator and play with the BC value until it matches the real world. I use this to estimate 300 and 400 yd drops, and am usually pretty close.

The only BC that matters is one determined as I do above. The numbers they publish are so far off I would never hit a target with them.

Also, scope height measurement etc get important as you get out to around 300 yds.

The real way to determine BC is to use two chronos, one at the muzzle and one at the target.