Robert, although there are obvious differences, the bolting system still strikes me as being similar to a Kersten. The outside end of the bolt (when it protrudes from the receiver) is even the same shape. The holes in the barrel extensions (they're not "rib extensions" like a Greener or a doll's head on a sxs) are certainly larger and of a different shape. But even when a sxs has a square rather than a round crossbolt, it's usually referred to as a "square Greener".