Some of the W-L that saw USMC service have modifications to the rear of the bolt.  There us a U-shaped piece of sheet-metal thickness steel that would protect the shooter if the striker were to be blown free. IIRC, it is spring steel and snaps into grooves machined into the rear of the body of the bolt.

If the USMC armorers had not encountered problems, that mod would not exist. 

That must have been an authorized mod and must appear in writing somewhere.