It looks like the one edge, from this picture, is irregular by having rusted or having been broken. I don't recognize this as any part of the Krag action at all. Must just have fallen in there or been placed in the action for some reason.

Does everything else work? Anything seem out of place?

Maybe someone else has an idea.

If not sure, take a variety of pictures of the action and we'll see what might be wrong or different, if anything.

Nice little mystery.