Shooters want a straight answer to the question: "How much BC gain from pointing?" Unfortunately, the answer is: it depends (a lot). Mostly it depends on the bullets you start with, and a little on the tool you use. It's understandable that people get different results when testing different lots of bullets with different tools, and the inconsistent results certainly don't imply that anyone's results are invalid.[emphasis added]
Perhaps, but they need explaining. To waste a little time, Bryan, I started this thread because reported phenomena did not match what the ballistics tools we have predicted. To use a different analogy, I have a long-standing, complicated medical issue. Last week, a new doctor said “It's all caused by a virus, probably one you got as a kid over 50 years ago.” Very medical. But if a 16th century priest said “It's all caused by demonic possession,” the only difference would be if current doctor can do something, or at least, predict the next step in the disease. Otherwise, demonic possession is just as good,
just as scientific an explanation as a virus.
Now that 18-inch high bullet strike has been around a while, and is often used as an argument for the benefits of closing meplats. Secondly, I know all the players, though some better than others. They are all reasonably serious, careful people. I would be stunned if Greg Sigmund (who made the bullets) released a run of bullets with a meplat significantly more open than normal. One of the things he has always taken pride in are the meplats of his bullets. I've know Jim Hardy a long time. Like most of us (certainly including me), he may not always be right in his conclusions, but his
observation statements can be deposited in the bank. I don't know Jason Baney well, but he doesn't seem the sort to accidentally tip the powder can during a test.
OK, there is an empirical phenomena. On the earlier thread, I had also mentioned that Dave Tooley, on seeing the Oehler/Bartholome raw data on long-range bullet performance, had purchased a Model 43 and done some work of his own. Where we started was looking at the extreme spread of BC in 10-shot groups. Several bullets/loads in the Oehler/Bartholome data had an ES of .020 for B.C. Looking only at the evenness of ES for BC, we quickly noticed that all the tipped bullets (A-max & perhaps a couple Nosler) had very low ES/SD with respect to BC. So as a first test, Dave set up to put the plastic tips in bullets. I know we tipped the 187 BIB and the 106 CR -- both of which I shot in competition, plus some bullets used at that time by Scott Fletcher and Steve Shelp. I don't remember if the tipped 106 CR's were ever run over the Model 43; I wasn't able to attend the test session. But in terms of height of bullet strike and group size, the tipped 106 CR I shot at 1,000 yards showed no increase or advantage over the box-stock 106s. To conclude the story, Trimming meplats, which also solved the problem of larger ES in BC, took a lot less time than inserting tips. Dave decided that the slight increase in BC from tipped bullets wasn't worth the effort, and came up with his meplat trimmer.
So Apples to a near-kin kind of fruit, we have conflicting data. Looking for any kind of explanation other than Greg Sigmund let out a really horrible lot of bullets (which would be very hard to believe), I asked Randy Robinett to compute the increase in BC if the meplats of
his bullets were closed from 0.050 to 0.010. I realize the JBM program wasn't designed to give accurate information/prediction with a change only at the point, but if making that change gave results in the general region, at least we'd have a place to look further. And it kinda, sorta did, except it didn't quite predict the entire gain, and as you point out, reshaped the ogive generally to get there.
I also remembered a statement of yours, that a bullet could be dialed in to a particular Mach number, and as I remember (could be wrong), you thought the shape of the ogive for that bullet would not be a simple tangent or secant. So I wondered if we had maybe stumbled on an instance of that.
So that was why I started this thread; you'll notice that the title is coherence amongst ballistics programs. Maybe most people will settle for “Better, I don't know why or how much, but I don't care.” I suppose I'd take it too, “better is always better” is a tautology. But I've also learned over the years that if we understand a phenomena, and can place it within a theory, we get a lot more “betters,” and faster.
So no, inconsistent results really do mean something is wrong, and if we can find it, we're better off. Especially if it leads us to a better model for ballistic theory.
