I've been searching for a BC for a friend who uses a Brooks Postell and the answer from most folks was in the 0.40 range which is quite compatible with the estimate in the thread posted above. That is darn low, but that seems to be the consensus.
If you wish to create estimates for yourself, you can do so if you can get the chrony data by using the following webpage. Once you have the BC, the website will also give you methods of calculating bullet drops out to any range given a zero at any specified distance...
http://www.eskimo.com/~jbm/index.html