I have no way of knowing who is right, the manufacturers or Litz, but he has a good reputation. As youstated, some bullets he indicates better than advertised BCs (180 an 200 Nosler AB) and others a little worse (185 Barnes TTSX and 225 Nosler AB). That is for the handful of .338 bullets I've looked at. Both the 180 and 200 AB really are notably better.
The 200 AB shoots well in my Kimber and thus may be the bullet of choice for next season. I'm loading some up with 8208 to take out in the cold and see how the velocity holds up.
