USGI bolt stops are cast, so the circle might be from a mold or tree. That would also be a possibility with this extractor.The only "O" marked M14 part I know of is on the bottom side of bolt stops, and those are H & Rs and it looks a little different. I don't believe it is USGI, SAI, or Fulton, that could be a help to it's identity.
I don't doubt that it is cast, I just don't think that mark is an ejector pin.Investment cast wax molds and MIM cavities normally have ejector pins.
Those pins show up as circular depressions of all sizes dependent on the part size.
The classic part for that here is the M14 bolt stop, that circle is the tell tale between
rolled bar stock and cast.
If anybody wants an explanation on "rolled bar stock" I will post it.
I was not referring to the extractor but cast parts in general.I don't doubt that it is cast, I just don't think that mark is an ejector pin.
They usually look more like this: