Receiver rail guide.

[sheepherder]

It's not all dependent on the ammunition. A weak recoil spring could cause excessive pounding on what I call the 'abutment'. Here's the areas I am referring to - yours compared to my commercial...

It looks like yours has taken a bit more hammering than the commercial...And yes, being hammered from both sides could cause that 'fin' to work-harden/fatigue and break...

There really isn't any other stress on these 'fins'...Under normal operation...

If it were my Luger, I would be concerned about the breech block cracking...

But everything is relative! If you're happy with the way it functions, then that's all that matters!