Huh? On the 1851, the plunger screw can only go in one way, since the loading lever is countersunk for the screw head. The early squarebacks had it going in right to left, but in all subsequent production it goes in left to right like the loading lever screw.
In the creeping rammer models, the plunger screw is almost always seen with the screw head on the left, but since it is the rammer that is countersunk, and since it can go either side up, the screw can go either way.
Jim