SR you lost me if the chamber is to long,
I should have said it is a long ways to the rifling area that the bullet contacts the Leade I think it is called and the chamber is not so long.
I am going to take more pictures of .308 chambers and cut the base of a case off and stick my camera in there and insert it into the chamber and see what kind of differences i can see with the case shoulder bottomed out in the chamber.