I found a picture of the plunger, in case anyone's not sure about what I'm describing. The groove in the extractor is a mystery to me. The design and orientation of the plunger suggests it would extend over the edge of the extractor and act as a brake. With the long edge oriented vertically on the muzzle end, I think that's exactly what it would do.
But if that's true, what's the groove in the extractor for? With the plunger oriented horizontally (or possibly vertically on the butt end), a corner of the long side would contract the very end of the groove. With the very limited amount of travel available to the extractor, I can't imagine more than 10% of the groove being used for travel. Seems like the designers would have set the plunger to contact the middle of the groove, if that was it's purpose.
I'm taking this to a local gunsmith that came highly recommended. However, I'm not sure he's ever seen a series 180. I'd like to be able to answer any questions he has.