The BS of Ballistic Coefficients

By Randy Wakeman

With rare exception, the ballistic coefficient (BC) numbers supplied by muzzleloading bullet manufacturers are horrifically flawed and bear little semblance to reality. The rare exception are the BC's provided by Olin / Winchester, based on 200 yard averages of live fire on their own in-house Doppler radar range.

It can be intriguing to use ballistic software programs to come up with a general idea of wind drift, vertical trajectory and terminal energy, but without an exact muzzle velocity and somewhat realistic G1 drag coefficient (BC), the task is impossible. Added to this mess, saboted projectiles operate at a very low BC right in front of the muzzle before the bullet fully escapes from its shoe. The BC of the bullet "itself" is no good, as it is always fired with the sabot.

Any published BC is only tenuously linked to trajectory and terminal energy, anyway. With the endless variations in velocity in a specific gun and the equally infinite variations in ambient conditions, they can at best be considered only as a vague guide. Certainly they are no substitute for testing in your own gun. That said, the use of reasonable, conservative ballistic coefficients will not result in a twisted conception of range and energy. Taking inflated BC numbers as absolutes can do just that.

In my own testing, and comparing notes with colleagues, I've found that by using a specific brand of software based on bullet factor, specifying a #2 ogive, caliber, weight, and muzzle velocity, the results yield a close approximation of real world 200 yard average BC's. Best of all, the dumb old piece of software does not read ad copy, hyperbole, or any other nutty claims. It does not care who made what, and the values it generates are not at all random. The numbers comport closely to actual field results from the Hornady SST's, T/C Shockwaves, and PR Bullet Dead Center bullets. Following are some realistic BC numbers. (All values are based on a 2100 fps muzzle velocity.)

    195 grain .35 caliber sectional density = .227, BC = .267
    200 grain .40 caliber sectional density = .179, BC = .211
    220 grain .40 caliber sectional density = .196, BC = .231
    240 grain .40 caliber sectional density = .214, BC = .252
    260 grain .40 caliber sectional density = .232, BC = .273
    250 grain .429 caliber sectional density = .194, BC = .228
    300 grain .429 caliber sectional density = .233, BC = .274
    250 grain .45 caliber sectional density = .176, BC = .207
    300 grain .45 caliber sectional density = .212, BC = .249
    340 grain .45 caliber sectional density = .240, BC = .282

Compare it yourself to your own chrono-to-chrono work, and actual drop results. I think you will be surprised, if not astonished.

If the above reality check numbers are disappointing to you, you can take some comfort by comparing them to a 177 grain, .50 caliber round ball (.490). This genteel gyroscopic gem has a sectional density of .105, and a ballistic coefficient of .068.

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Copyright 2004, 2012 by Randy Wakeman. All rights reserved.