Mac,
You'll find I don't do 'drive by'. My absence has been due to the fact that I responded to this thread just before leaving for a week-long shooting tournament; I got to the range late that night. The match was delayed yesterday due to rain so we had a late finish and I didn't check this thread. Today we finished on time so this evening is the first chance I've had to re-visit the conversation.
Sorry if I mis-understood your point in the first thread. I can see clearly now that you're not disagreeing that G7 referenced BC's are superior to G1 BC's for modern long range bullets. It seems your major concern is the method by which BC's are determined. We agree that the method that Ken describes is good, but possibly for different reasons.
I like the tof method because it's far more practical than measuring downrange velocity (chrono strikes are expensive, etc). Also, maximizing the range over which you measure tof is important for reducing experimental error. Both these reasons have to do with practicality. If you have methods/techniques that you have found work better for testing large numbers of bullets for BC I would be interested in hearing your results.
You indicated not having the second edition of my book yet. There's an addition to the BC chapter that is relevant to this discussion; here�s a summary. An experiment was conducted as follows: chronograph at the muzzle, and a tof sensor at 1000 yards
in addition to a special chronograph at 1000 yards. For each shot I derived a G1 and a G7 BC from both the tof and the velocity decay data. Summary of results: the bullet that looked most like the G7 standard (Berger 155 VLD, Dyer 155 HBC) had derived G7 BC's there were nearly identical from the tof and velocity data. However, the G1 BC's were quite different for the tof vs velocity data. These �G7� bullets had drastically different G1 BC�s depending on if you derived them from tof or velocity. Bullets that were shaped a little different from the G7 standard (examples are tangent ogive bullets like the 155.5 FULLBORE and 155 SMK) had G7 BC�s that were similar, but not quite the same, and G1 BC�s that were still quite different. The conclusion from this data which I find interesting and relevant to this discussion is that:
when a bullet is shaped similar to the standard projectile for which you�re referencing it�s BC to, the BC you derive will be less sensitive to the method used to determine it.
I think this addresses your statements about BC testing methods, and the places in which G1 and G7 BC�s are similar, but I�m not sure. To be honest, it�s been difficult for me to nail down what your position is exactly. You said that you aren�t contesting that G7 BC�s are better for LR bullets than G1�s, but you disagreed with my assessment that the paradigm toward G7 BC�s will continue. This is confusing.
I agree that the method Ken described for determining BC�s from raw data is a good method for both academic and practical reasons. But this does not support the statement from your original post that:
Apart from magnitude, apparently the drag characteristics of supersonic flight are insensitive to bullet shape. Thus, you can't look at the shape of a bullet and tell which standard projectile it best matches in supersonic flight as it doesn't seem to matter much what the shape is.
The drag characteristics of supersonic flight
are most definitely sensitive to bullet shape! You point out that for a specific velocity range the curves are similar in shape, but they diverge at faster and slower speeds for the different (G1 vs G7) shapes. Most of our LR bullets, even those without secant ogives, are much better matches to the G7 standard than G1. In light of this fact, I find it hard to accept your above quote, as well as the claim that you�re not advocating G1 as a reasonable standard for modern long range bullets.
I think you give �the industry� too much credit when you imply that their reluctance to adopt the G7 standard has anything to do with scientific reasons, and more to do with marketing. Of course it�s possible for someone to advertise a G1 BC that was averaged for the exact velocity range that a shooter needed it for, and for a shooter to hit a target with that BC. However, I ask, what happens when the bullet doesn�t stay within that speed band? The prediction goes to crap, that�s what.
In closing, I�m not interested in arguing about the best way to manage the problems of a clearly non-representative (G1) standard. If you want to go on talking about the best way to use G1�s for long range bullets, and postulate that they might be effective it used properly (which the industry has clearly demonstrated that they won�t), then I won�t comment. I also hold to my belief that in time the paradigm will shift because using representative standards is less sensitive to the methods used to derive BC�s, and therefore more useful for doing predictive analysis.
One further comment to those who commented on the �shoot and spot� hunters. No doubt this is an effective method for getting on target at long range: make a somewhat educated guess; shoot; spot the miss, and adjust for the next shot. Provided the game animal doesn�t spook and prevent a follow up shot, this can work. However, this isn�t what this conversation is about. This conversation is about representing the trajectory of the bullet
before it�s fired so that a first shot can be on target.
Any idiot with a spotting scope can get a shooter on target. But it�s the science of ballistics and the shooters ability to apply it that will enable first round hits. This isn�t meant to be an insult to anyone, just a definition of the purpose of ballistics; which is to be predictive, not reactive.
-Bryan
