I know that this thread is old, but I hope the thread starter will see my reply. I have one of the small ring Mexican Mauser's in .257 Roberts Improved, and I am exploring this matter on another board. It seems that the barrel lug is smaller than other small ring Mausers while ring diameter remains the same. This would make the Mexican Mausers stronger than other small ring Mausers. I should know just how much stronger in a very short time.