That pin does look broken, since they have no spring on the firing pin, you should see it poke out of the bolt if you point the muzzle down with it in the gun. And yes, that is indeed a 520, one of the earlier ones with the humpback receiver that I mentioned earlier. That pin does look different than the one in mine; May want to check with these guys to see what they have: Savage Shotgun Parts, Stevens Shotgun Parts,Springfield Shotgun Parts, Original Obsolete Stevens Shotgun Parts. Stevens Autsomatic Shotgun Parts, Stevens Pump Shotgun Parts, Stevens Single Barrel Shoptgun Parts, Stevens Shotgun Barrels, Stevens Doubl. You user name wouldn't have anything to do with New Castle, PA would it?