We're on the same page for the most part. I only took issue with your treatment of BC's as a useful concept because you seemed to imply that BC's weren't 'good enough' for general use.
As far as 'tweaking' BC's to match observed
trajectories, I have to raise a caution flag there as well.
There are many variables that can make it look like
the BC is in error, when in fact it's something else. For example, a common one is scope reticle movement. If the program predicts 10 MOA of drop and you dial your scope 10 MOA and hit low, well, the BC must be
off, right? The serious shooters here on LRH know better but many shooters are quick to question the BC because it's the most mysterious and (generally) the least understood variable. You can 'tweak' the BC to get it to make up for an out-of-calibration scope, but it won't really be right. You end up chasing your tail by defining multiple BC's to make up for the scope error, and in the mean time your predicted impact velocity, energy, wind drift, etc are all in error because you're feeding the program a false BC to force it to match the skewed drop values resulting from the out-of-calibration scope.
The out-of-calibration scope is just one example of a common error source but there are many others that tempt people to 'tweak' BC's to match their observed
Even having said all that, I acknowledge that there are still some cases where a certain rifle with a certain barrel will fire a bullet in a way that slightly affects the effective BC that bullet flies with. Variations in BC tend to be small for accurate rifles. If too much yaw is induced, or too much surface scaring, etc, the rifle will probably not be accurate by our standards.
As to the test results from the original poster, I can't remember the details now, but when questioned, I seem to remember some missing information like some key atmospherics, or velocity measurement, or something that the measured BC's were based on. No disrespect to the tester, but truly accurate BC testing is HARD. Even if your test procedure is sound, you can easily have instrumentation error that you don't know about. Is your Kestrel
calibrated? How do you know your chronograph is accurate? What about your laser rangefinder? When you test BC's, every single variable has to be known to a high degree of certainty or the error will compound on the final result.
I do think that unique drag functions are useful for those projectiles that remain comfortably stable thru transonic. If the bullet exhibits low pitch/yaw, then it's trajectory can be predicted quite well at all speeds, but most bullets fly unpredictably at transonic, making prediction a futile effort.
Thanks for the healthy exchange Lou. Always good to investigate and discuss alternate approaches.