Thanks for the reply. Most of my testing is done in some riverbottom farmland in south central Ohio, at just a few hundred feet ASL. I note altitude, but use the actual temp, press, and hum of the day to calculate air density rather than assume standard conditions for altitude.
I will continue to study the yaw effects. It's a very interesting challenge because it might not be totally repeatable for every rifle. My original assessment is that there cannot be significant levels of yaw (enough to affect BC) because such yaw levels would cause tremendous dispersion. In other words, in order to get a 2% reduction in BC, there would have to be so much yaw that groups under 5 MOA would be impossible. (you can read a write up about this on my website:
Homepage of Bryan Litz - A Bravenet.com Hosted Site
Look at the "Ballistic Coefficient Testing" article linked on the left.
I may have to revise those conclusions because apparently, there can be a substantial reduction in BC without accuracy going completely to hell. I'll have to revisit the modeling to see what mechanism makes this possible.
The new BC's for the 130 and 140 VLD's are (average from 3000 fps to 1500 fps):
6.5mm 130 grain VLD: 0.552 (just 4% lower than what you found)
6.5mm 140 grain VLD: 0.595
These two are being decreased about 7-8% from their original values, which is a large change compared to most others.
They are still the highest BC bullets in their weight class. For comparison, I measured the 142 SMK at .588, which is just 2% higher than their average
The 139 Lapua Scenar measured at 0.557, which is 10% lower than their advertised BC (I think my lot of Scenar's for this test had a larger than average meplat).
The 140 Amax measured at 0.584, which is 6% higher than their advertised BC.
These BC's are completely consistent with common sense if you simply line these bullets up against each other and consider the profiles, and account for a few grains difference in weight.
The Berger VLD's (130's and 140's) were interesting because they had the exact
same form factors (drag). This means that the difference in BC is completely do to the difference in weight between them. In other words, the 140 VLD is 7.7% heavier than the 130; and so the BC is exactly 7.7% higher. This wouldn't be true if the drag were different between the bullets but it is. Just an interesting note. The 7mm 168 and 180 grain VLD's are the same way.