graybeardtmm3,
Yes, I'm sure that is what the patent is for. As is shown in the photo above, the opening for the barrel lug is not centered. The "hinge pin" is not a common "Pin" at all it is (I believe) an axel (as you described) milled from the action, and is larger, thereby providing a larger wearing surface. I have a couple other Jager single shot tip up rifles that are not the same as this one. If not rare, I think single shots on this patent are uncommon.
Mike