Thread: Interesting study on Ballistic coefficients.

As the title says, worth a read.

http://www.dtic.mil/dtic/tr/fulltext/u2/a554683.pdf

http://www.dtic.mil/dtic/tr/fulltext/u2/a555975.pdf

The second paper is more useful as it has experimental data.

I had always thought the Nosler G1 BC for their 7mm 140gr ballistic tip was too good to be true.

You're onto a loser from the start working with G1 BC. If you want to be fussy you need to use G7.

Also you need to look closely at the velocity ranges you will be using because BC varies quite a lot. Charitably, this may be the origin of some out of whack published BC figures as BC is higher at higher velocities.

Litz only tested 120 gr and 150 gr BT bullets so I estimated a G7 BC for the 140 gr at 0.214, assuming that it has a similar form factor to the 120 and 150 (ie 1.15 and 1.163 so I used 1.16 for the 140.

Even a chronograph has some error of measurement. And, as shown in these two papers manufacturers' published BC are not completely accurate.

So, my conclusion is that you need to shoot your own rifle at several ranges and determine your own BC and MV values using published and chrono values as a starting point. I'd adjust the BC more than the MV and try to get a predicted trajectory that matches my observed one. The ballistic program should only be used to estimate trajectory between ranges you have shot yourself.