ok what does this Michael make ?
I am a scientist. The history of science and scientific method both reveal characteristics of an adversarial process when experiments are compared with theoretical models and when experimental results are compared with each other.
In every case, clarity regarding whether published numbers are the result of a careful experimental measurements or the result of theoretical predictions is essential to scientific integrity. Berger seemed to be moving its BC numbers toward experimental measurements with Eric Stcker's 2009 post on why they changed their published BC specifications, so it is disheartening for me to learn five years later, that 30 or so of their improved BCs published at that time were likely based on theoretical predictions, when his post gave every impression that the published specs came from firing measurements.
When disagreement between theory and experiment or one set of experimental data and another occur, the more productive scientific process is to dig into the details and try and figure out the causes of the differences. In the BC world, this means careful review of the experimental methods and sources of uncertainties. It also means giving some consideration to whether the different results may be attributable to lot to lot variations or variations in the rifle barrels used in the experiments.
When noting that Bryan has often found different BCs from Sierra for Sierra bullets, I am not to quick to trust one BC measurement over another, but rather to keep an open mind and consider likely sources of the discrepancies. It is notable to me that Sierra's original BC measurements were made many years ago, and certain processes may have changed over the years. It is also notable that (unlike comparisons with some companies) the discrepancies seem to be spread evenly with Sierra's BC numbers being lower than Bryan's about as often as they are higher. Is the Litz method so superior to Sierra's that one should regard the resulting BCs as more accurate? I don't know. After reviewing both methods in careful detail, I think the next steps in answering these questions are shooting the same lot of bullets through the same barrel using the two different methods.
The application of the scientific method to product quality is of great importance in DoD procurement in ballistics and many other areas. Over the past 13 years, we've been working hard so that companies that demonstrate sleight of hand in substituting model predictions for measured product specifications do not receive taxpayer funds through lucrative DoD and government contracts. DoD has been moving over the past decade to integrate more commercial off the shelf (COTS) products into their supply chains, and consideration of a company's track record providing accurate product specs to the consumer can be an important indicator and prevent the DoD from mistakes that cost the taxpayer millions.
For example, the contract for the .300 Win Mag sniper ammunition brought in $45 M for ATK and utilized COTS components. The fielding of this ammunition was a success due to the folks at NAVY Crane's careful selection of proven components (SMK 220 grain bullet, H1000 powder, etc.), establishing rigorous product specifications, and designing a test protocol to ensure that the product continued to meet its specifications during its life cycle. Yes, this ammo can likely be improved through the selection of improved components.
In addition to finding some discrepant measurements on Berger's varmint bullets, we have also measured BCs lower than Berger's claims for the 155.5 .308 Fullbore bullet and the 168 grain VLD. For example, we've consistently measured a G1 BC of 0.406 to 0.409 for velocities near or below 3000 ft/s. We've gotten a BC as high as 0.444 at higher (.300 Win Mag) velocities, but nowhere near the 0.464 advertised by Berger in the velocity range (3000 fps and down) where these bullets are expected to be used. We've measured the BC of the 168 grain .308 VLD to be 0.421 at a near velocity of 2620 fps. Berger's spec over the range of 1500-3000 fps is 0.473. Considering the velocity issues does not resolve the problem, because Bryan's book actually shows BCs of 0.489 and 0.510 at 2500 and 3000 fps respectively.
If you look at the graph carefully (p 462), you'll see that Bryan's method only actually determined the drag coefficients from M1.8 to M2.4, and there are only eight points on the graph, indicating either drag measurements of four bullets at two velocities each or (more likely) two bullets at four velocities each. Since the experimental data only covers a range from about 2000 fps to 2600 fps, one wonders what kind of extrapolation is being done to determine BCs from 1500 to 3000 fps. The extrapolation for the 175 grain Long Range BT (p 463) is even bigger. The data in the graph shows drag coefficients from M2.1 to about M2.35 (roughly 2400 fps to 2600 fps), yet the table shows BC determinations from 1500 for to 3000 fps.
So, the questions extend beyond the flat base bullets and include the boat tail bullets also, but my hope on this thread was to focus the discussion on the bullets for which Berger is advertising BCs which they may not have measured at all.
