The
B.S. of Ballistic Coefficients
With rare exception, the ballistic coefficient 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, the equally infinite variations in ambient conditions; at best they can be considered only a vague guide: no substitute for live testing in your own gun. That said, the use of reasonable, conservative ballistic coefficients cannot 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 startlingly close approximation of real world 200 yard average BC's. Best of all, this dumb old piece of software does not read ad copy, hyperbole, or any other sometimes nutty claims. It does not care at all who made what, but the values it generates are not random at all-- and their numbers comport closely to actual field results from the Hornady SST's, T/C Shockwaves, and PR Bullet Dead Center bullets.
All values are based on a 2100 fps muzzle velocity.
195
gr. .35 caliber sectional density = .227, BC = .267
200 gr. .40 caliber sectional density = .179, BC = .211
220 gr. .40 caliber sectional density = .196, BC = .231
240 gr. .40 caliber sectional density = .214, BC = .252
260 gr. .40 caliber sectional density = .232, BC = .273
250 gr. .429 caliber sectional density = .194, BC = .228
300 gr. .429 caliber sectional density = .233, BC = .274
250 gr. .45 caliber sectional density = .176, BC = .207
300 gr. .45 caliber sectional density = .212, BC = .249
340 gr. .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.
Postscript:
It is not realistic to list ALL the "as tested" ballistic coefficients vs. the fantasy published by many bullet manufacturers. One would hope that it would be their job to "get honest," and offer some TRUTH in advertising. That is unlikely to happen in the smokepole city. Here are just a few eye-openers, though:
Actual 100 yard BC's as tested pushed by 100 gr. T 7 :
PR BULLET QT 215 gr. = .174 PUBLISHED BC = .319
PR BULLET DC 200 gr. = .176 PUBLISHED BC = .300
PR BULLET DC 220 gr. = .192 PUBLISHED BC = .325
PR BULLET DC 240 gr. = .211 PUBLISHED BC = .351
250 Hornady SST = .184 PUBLISHED BC= .210 by Hornady, .240 by Thompson / Center (same bullet!)
300 gr. Hornady SST = .226 BC PUBLISHED BC = .250
© 2004 by Randy Wakeman
