They are not the same chamber but they are so close that the difference is irrelevant. They are cross compatible and I actually find the .264LBC chamber to be a tad more accurate and easier on the brass necks. So one could think of the .264LBC as the match version of the 6.5grendel. Bill Alexander is not going to tell you this for obvious reasons but anyone with experience in reloading and ballistics that is impartial to the subject will tell you it is 101% ok to shoot 6.5grendel in a LBC chamber. The hornady 6.5 Grendel 123gr is extremelly accurate shot out of a good 264LBC barrel. My opinion is based on my experience shooting from both chambers and not what I read online.