Eagle, That was my thoughts as to the "blowout" star on the rib.

What appears as a small protrusion on the barrel looks to samll to be a bayonet lug or anything else. Is it a plug that hasn't been filed away??

To me, it seems that the star on the rib is a potential concern; ie, that one of the barrels has a pinhole and that the star is the visible sign of the pinhole.