I'll take another whack at this since even my "Cliff Notes" explaination appears to have been too wordy.

Shooters (and mostly the Military) has tried to come up with a way to predict the flight path of projectiles.

One method has been to express bullet flight in comparison to a known standard. The known standard for years has been the G1 Standard Projectile which as earlier mentioned is a 1lb, 1 inch in diameter, etc. projectile. The flight properties of this Standard Projectile(mostly loss of velocity after firing) was measured in actual firing initially in the 1880's through the 1940's.

BC's are a number of how well a given bullet performs compared to the Standard Projectile (usually the G1).

Part of the reason why actual firing doesn't always match up to tables or computer generated numbers is that many are based on the G1 Standard Projectile which doesn't accurately reflect the profile of today's sharp pointed, boat tailed bullets.

Hot Core, I actually agree with you regarding determining BC. BC is just a number...an estimate. It's far better in practical terms to do actual firing, not to determine BC, but to produce your own drop tables to know exactly where your rounds will impact (and to determine the accuracy of your rifle/load at the actual ranges you hope to fire at).

With that said, I have had occasion to use wind charts that were computer generated off of BC's in competition where no sighters were allowed and I had little time on the trigger with a new load. There were wind meters galore on the line giving readings and the wind chart allowed me to put my string in the 10 ring at 300 yards.

"Ballistic coefficient" is more or less based on a standardization of a given manufacturers ballistic facts and figures that is intended to make ballistics computable without the physical testing. They figure theyve dont enough of that by now, but with radical new designs they still need to anyway to develop a primary data base.



As I see it, the fault in this concept lies in that there is not a single entity that compiles the data such as Saami, but rather various manufacturers such as Nosler and Speer base their assigned BC #'s on their own findings, and therefore the BC values given to bullets and each manufacturers reference charts are NOT interchangable. IMHO some manufacturers are overly generous in assigning BC values to their bullets as a sales ploy whereas others are more down to earth. This can easily be reckognized with a simple comparison of brocures. Otherwise it is basically a sound concept.

The Ballistic Coefficient of Rifle Bullets

By Chuck Hawks






Ballistic Coefficient (BC) is basically a measure of how streamlined a bullet is; that is, how well it cuts through the air. Mathematically, it is the ratio of a bullet's sectional density to its coefficient of form. Ballistic Coefficient is essentially a measure of air drag. The higher the number the less drag, and the more efficiently the bullet cuts through the air. So for purposes of flying through the air efficiently, the bigger the BC number the better.

BC is what determines trajectory and wind drift, other factors (velocity among them) being equal. BC changes with the shape of the bullet and the speed at which the bullet is traveling, while sectional density does not. Spitzer, which means pointed, is a more efficient shape than a round nose or a flat point. At the other end of the bullet, a boat tail (or tapered heel) reduces drag compared to a flat base. Both increase the BC of a bullet.

For example, a Hornady 100 grain round nose 6mm bullet has a BC of .216; a Hornady 100 grain spire point 6mm bullet has a BC of .357, and a Hornady 100 grain boat tail spire point 6mm bullet has a BC of .400. All three of these bullets have a sectional density (which is the ratio of a bullet's diameter to its weight) of .242, because they are all .243" in diameter and weigh 100 grains. But the more streamlined bullets have a higher ballistic coefficient. They are the ones to choose for long range shooting where a flatter trajectory is important.

To illustrate the practical difference between these three styles of bullets, let's use Hornady's trajectory figures for the 100 grain 6mm bullets above. Starting all three bullets at a muzzle velocity of 3100 fps from a scoped 6mm rifle zeroed at 300 yards, the trajectories are as follows.

.243" 100 grain Round Nose (BC .216): -1.5" @ muzzle, +4.8" @ 100 yards, +6" @ 200 yards, 0 at 300 yards, -15.9" @ 400 yards, -46" @ 500 yards.

.243" 100 grain Spire Point (BC .357): -1.5" @ muzzle, +3.8" @ 100 yards, +4.7" @ 200 yards, 0 @ 300 yards, -11.1" @ 400 yards, -30.5" @ 500 yards.

.243" 100 grain Spire Point BT (BC .400): -1.5" @ muzzle, +3.6" @ 100 yards, +4.4" @ 200 yards, 0 @ 300 yards, -10.4" @ 400 yards, -28.6" @ 500 yards.

There is a pretty big difference in trajectory between the round nose bullet and the two pointed bullets, making it obvious why it is folly to choose a round nose bullet for long range shooting with a high velocity rifle like a 6mm Remington or .243 Winchester. Also notice the big difference in BC between the round nose bullet (.216) and the spire point bullet (.357).

But there is less difference between the trajectory of the flat base spire point bullet and the boat tail spire point bullet. The boat tail helps, but not nearly as much as the point on the front of the bullet. The boat tail bullet had .3" inch less rise at 200 yards, and 1.9" less fall out at 500 yards. These differences are real, but unlikely to make or break a shot at a big game animal. This is shown by the smaller difference in BC between the two pointed bullets, .357 for the flat base and .400 for the boat tail.

To further assess the importance of a boat tail, note these pairs of Speer spitzer bullets of the same weight and caliber. In each pair, the first bullet has a flat base, and the second has a boat tail.


.243" (6mm) 100 grain, BC .351
.243" (6mm) 100 Grain BT, BC .430

.257" (.25) 100 grain, BC .369
.257" (.25) 100 grain BT, BC .393

.277" (.270) 130 grain, BC .408
.277" (.270) 130 grain BT, BC .449

.308" (.30) 165 grain, BC .433
.308" (.30) 165 grain BT, BC .477


A list of pointed (spitzer type) hunting bullets considered a good bet for long range shooting in their respective calibers, with their ballistic coefficients, follows. Boat tail bullets are designated "BT," all other bullets have flat bases.

All of the figures that follow are taken from the Speer Reloading Manual Number 13. The same weight bullets from other manufacturers will have different BC's, because they are slightly different shapes. But these Speer numbers are as typical as any, and being from the same source they are useful for purposes of comparison.


.224" (.22) 55 grain, BC .255
.243" (6mm) 90 grain, BC .385
.243" (6mm) 100 grain BT, BC .430
.257" (.25) 100 grain BT, BC .393
.257" (.25) 120 grain BT, BC .435
.264" (6.5mm) 120 grain, BC .433
.264" (6.5mm) 140 grain, BC .496
.277" (.270) 130 grain BT, BC .449
.284" (7mm) 145 grain, BC .457
.308" (.30) 150 grain BT, BC .423
.308" (.30) 165 grain BT, BC .477
.311" (.303) 150 grain, BC .411
.323" (8mm) 150 grain, BC .369
.338" (.338) 200 grain, BC .448
.375" (.375) 270 grain BT, BC .429

Note that with bullets of the same weight and style, such as the 100 grain .243" and .257" bullets or the 150 grain .311" and .323" bullets, the smaller diameter bullet always has the superior BC due to its better sectional density.

As examples of very streamlined bullets, note the BC of these Speer match type bullets. These are all pointed hollow point, boat tail bullets.


.224" (.22) 52 grain Match, BC .253
.284" (7mm) 145 grain Match, BC .465
.308 (.30) 168 grain Match, BC .480
.308 (.30) 190 grain Match, BC .540

Note that in the .308 pair, the heavier bullet (which has the greatest sectional density) has the better BC. The extremely poor SD of the .224" bullet lowers its BC, even though its shape is similar to the others.

Which explains why .22 bullets drop so much at long range and are so subject to wind drift, compared to larger caliber bullets with superior sectional densities (and hence, BC's). At a MV of 3100 fps a .224" Speer 52 grain BTHP Match bullet zeroed for 300 yards has a 500 yard drop of -43.9 inches, not much better than the 6mm round nose bullet in our trajectory examples near the beginning of this article. An interesting subject, this ballistic coefficient, and worth paying attention to when you select a bullet (or a caliber) for long range shooting.

A minor and almost irrelevant point these days with all the ballistic programs out there:



C=W/(IxD^2)



Where C = ballistic coefficient

W = weight in pounds

I = form factor

D = diameter



The benefit of looking at the formula is mostly to understand the relationships between it's components. You will note that W is the numerator, thus there is a direct proportional relationship between W an C, or more correctly C and sectional density, which is factored into the equation by the inclusion of D. Some assume that if you have the same form, or shape on two bullets that the BC is the same, which is not correct. Weight increases by the cube of diameter in a sphere while drag increases by the square, all things being equal. This plays on conicals as well but the weight will actually increase at a higher ratio, since drag on the shank is negligable, and on the base it is only a small fraction of total drag.



You may find representations of forms in Hatcher's Notebook, and other dissertations on ballistics I'm sure. Attempting to use such information as a means to calculate BC's is at best a tedious exercise which will render information of questionable value. A better approach is to shoot and observe, then perhaps fiddle with one of the online ballistic programs, which may in fact allow you to define your actual BC for the conditions in place at the time you shot the gun. Tomorrow is another day.



Don't fret too much about this. It is good to understand what's going on with your guns, inside and out, but for practical purposes BC does not have substantial impact inside of 300 yards for a rifle shooter. Beyond that, yes.

It is a numerical expression of a bullet's ability to overcome air resistance. Ballistic Coefficient is expressed as a percentage of the ability to overcome air resistance possessed by a "standard" bullet, such as the "Krupp standard projectile", which has a B.C. of "1". (There are other "standard" projectiles.) The great majority of small-arms projectiles have a B.C. of LESS than 1. In fact, every small-arms bullet I am aware of has a B.C. of less than the standard projectile. However, some of the V.L.D. bullets come close, like 0.73% of the standard.



There are two ways of determining the B.C. of a bullet. One is to multiply the sectional density of the bullet by its' "coefficient of form" (a numerical value assigned to the "pointedness or lack thereof" of the bullet. (Ogive shape & meplat size.)



The other method, and by far the best, (probably the only way to get a true B.C.), is to chronograph the bullet near the muzzle, and again downrange at least 100 yards from the midpoint of the muzzle chrono, and determine how much velocity the bullet lost in that distance. You should know that the B.C. of any bullet varies depending upon the velocity it is travelling, and interestingly, some have higher B.C.s at higher velocities, and some have higher B.C.s at LOWER VELOCITIES! So as a bullet leaves the muzzle and slows down, its' B.C. changes in flight! Some get better, some get worse!