I don't think anyone is attacking Litz' numbers. BC values will change from rifle to rifle. Individual rifling dimensions and the resulting engraving on the bullet will affect BC, so when a bullet manufacturer or third-party ballistician publish numbers, they are 100% applicable only so far as the testing/calculation techniques and test rifles used. Litz' testing uses the most advanced methodology that I'm aware of, which is why his numbers are the most universally applicable. But the actual BC value from your specific rifle may differ slightly.
The only trouble with determining the BC difference, is getting accurate and precise measurements on velocities and bullet drop at range. Often when a guy thinks his bullet's effective BC varies from what is published, what's really going on is that his chronograph has a 1% error resolution, or his rifle isn't accurate enough to determine drops with enough precision to identify any small difference in BC.
