I suppose if one tries Hard Enough anything & everything can be discredited. It seems to me though that even if the sidewalls of the case had full adhesion the case head itself would have more rearward expansion than the barrels have radial expansion. Understand I'm not denying that radial expansion exists, but steel is stronger than brass. I simply do not think that it can be denied that a back thrust is applied to the breech/bolt of a gun. Simply too much evidence of it to throw it all out. As noted radial expansion doe not account for a blowback mechanism operating, Back Thrust does.
