View Full Version : Ballistic coefficients

January 9, 2000, 04:02 PM
First, what do they mean? What information do they convey? Second, how do I figure them out and calculate them? Thanks yet again!


Art Eatman
January 9, 2000, 05:54 PM
The ballistic coefficient has to do with a bullet's efficiency in flight. Or, "how it penetrates the air". For different shapes of bullets, think of comparative streamlining on cars or airplanes.

The Sierra reloading handbook has an excellent section on the meaning of b.c. and how to calculate the b.c. for a bullet. More importantly, it has tables already calculated :) for bunches of calibers, shapes, and weights.

The higher the coefficient, the lower the drag and thus 1) a flatter trajectory; and 2) more remaining velocity at a longer range.

Hope this helps,


Al Thompson
January 9, 2000, 06:17 PM
Art is right. (as usual) :)

IMHO, coefficent is almost a waste of time for anyone but very serious longrange shooters. (+ 600 yards) There are several other factors that weigh in with much higher payoffs. (accuracy, sectional density and trajectory)

The other problem is that through spark photography and testing, it's fairly well proven that the actual coefficent of a given bullet is effected by your (individual) rifle. (smoothness of the bore and rate of twist)



January 9, 2000, 06:41 PM
Thanks mates, I knew I could count on ya for the scoop! I appreciate it as always. I sure would like to know how many people here have doctorates and so forth!


Art Eatman
January 9, 2000, 07:14 PM
Hueco, it's not so much "doctorates" as out-living our enemies. :) And beaucoup "meddlin'" with this stuff for longer than I care to think about.

:), Art

January 9, 2000, 07:24 PM
I've read a couple of articles about ballistic coefficient in the past couple of years where the experimenters measured the muzzle velocity with a chronograph, and recorded it downrange with a second chrono. The actual BC can then be calculated with a formula using the velocity remaining and the distance. Derrick Martin of Accuracy Speaks, in Mesa, Az. did it with the second chrono placed at 500yds. I'd love to find the actual BC of several of my favorite bullets in this way, but none of my friends will lend me their chrono's to put downrange! Interestingly, Sierra rates their 22 cal. 80gr.MatchKing at .420, while Derrick's tests showed it with a BC of close to .480. Sierra's ballistics gurus explain it this way. The BC of a given bullet will change with atmospheric conditions and altitude. So, even if you take a computer to the range with you, and the best ballistics program in the world, you'll still be using a SWAG(Scientific Wild-Ass Guess)trying to come up with the exact trajectory of your bullet.

January 9, 2000, 08:03 PM
Ahhh, but BC changes with velocity (as does the speed of sound with altitude & temp) & does so with varying percentages based upon the bullets shape.

& Gizmo, trajectory is a function of BC (higher BC = flatter trajectory - all things being equal). Plotting through a ballistic program shows some pretty interesting trends.
& higher retained velocity based on a higher BC translates into more punch. I agree that for most applications, it has no real bearing, but I shoot two .30 caliber firearms around 2400fps & the difference between boattail & flatbase is fairly pronounced - 2-3" at 300yds. Enough to go with the higher BC bullet.

OK, Hueco, now start another topic on sectional density and terminal ballistics. ;)

& BTW, no doctorate but I have been caught playing at it in my younger years. ;)

January 9, 2000, 09:52 PM
Yes, I know this should be in the General board, but we have a nice discussion going here...and besides, it's convenient. Now, I have a question or two. Since I am really enjoying ballistics, and I am not at all bad in mathematics, is there a career here -- possibly somehow in law enforcement? Would it be a good idea to get an engineering or physics degree if I want to be a detective? "Twak amongst yaselves" and let me know of your thoughts. Thanks guys...again.


Tom D
January 9, 2000, 11:30 PM

Get a copy of "Understanding Ballistics" by Robert Rinker. If you are interested in understanding this stuff you will find it very enjoyable to read. I know Sinclair carries it. 212-493-1858, lists for $20 in their catalog.

[This message has been edited by Tom D (edited January 09, 2000).]

January 10, 2000, 12:05 AM
Hi Hueco

Are you from Texas?

I'd like to second the two suggestions already made for studying ballistics. I have both the Sierra reloading manual and the book by Robert Rinker. I believe you would enjoy perusing both of these references.


Long Path
January 10, 2000, 10:24 AM
References any bullet to the "Standard Bullet." Any good reloading text will have a section in the front on B.C. (Esp. Speer, Hornady, Sierra). Another interesting source that makes for fascinating reading is Hatcher's Notebook, by Major General Julian Hatcher. No kidding, this thing is a real page-turner! Things learned in 1930 are still very valid today, with regard to ballistics.

Long Path

Will you, too, be one who stands in the gap?


January 10, 2000, 08:02 PM
I love you guys! I assume you are not jokin gabout your interest in ballistics. But if you are...ooooh you are in some trouble!! heh-heh I have a real fire lit under me about ballsitics. The interesting thing will be to see where it leads me to. Thanks for all the suggestions!