It would seem to me that under full recoil with a 'hot' load, the 'abutment' is being hammered from both sides...The breech block hitting it in front, and the rear toggle 'lip' hitting it from the rear...
It would be interesting to mic [measure the width with a micrometer] the 'abutment' of a severely hammered Luger (one with a chipped toggle axle pin and/or missing 'fins') to see how much it had shrunk from the hammering...
(Rich B goes into safe and starts jacking toggles back to check) 