There's something not right about that spent brass, they're swelled too much. Since you mention that the swell is not all the way around the case, I would say that if you cast the chamber with Cerrosafe, and measured it, you would find its obround, or elliptical, instead of round.
The reason the swelling starts a little past the extractor groove is that the base is solid thick brass around the primer, and then the body starts to form a tube little on up, where it starts to swell.
|