i have both a J P Sauer & a J P Clabrough which have pins here. In both cases they are the pivots for the cocking rods. The actual hinge pin likely stops at the slot for the cocking rod with the slotted screw visable on outside being merely a cover, though some cocking rods do arch over the hinge so it comes all the way through. Usually though, when you see it slotted for screw driver as this one is, it is not the actual hinge pin.

Miller/TN
I Didn't Say Everything I Said, Yogi Berra