[DonVoigt]

Under normal operation, those little projections do not touch the breech block itself.

Grinding them off intentionally is a practice I've not heard of before - I don't think such was ever an "approved" practice, JMHO.

If the projections did not serve a purpose they would not have been included in the design or would have been eliminated during production- they would simplify mfg. of both the extractor and the recesses in the bolt quite significantly.

I believe such purpose is to aid in retention of the extractor in the breech block; without them there is nothing to prevent the extractor from moving forward and out of the block except the curve of the projection under the cross pin. Of course later on the Swiss altered the design to a full circle for the pin- did they eliminate the forward projections ?

I don't collect Swiss lugers, so can't check an extractor for its shape; GT ? Luger doc ?

The chips in the picture are a well known type failure, but not one frequently encountered - it can only be caused by a major malfunction = a punctured primer/ruptured case and the resulting significant gas leak.