As originally designed by Alexander Brown the Rotary Bolt was intended to bear on both the lower & rear surfaces of the Rib Extension. Bearing on the lower surface of course kept the barrels closed, that on the rear was to hold the standing breech "Up TO" the barrel breeches, helping absorb the axial load.
Several yeas ago a discussion of this came up here on the board. A number of Smith owners did a "Smoke Test" of the fit of their rotary bolts. As I recall None found a fit to the rear thus negating that function. In this case the entire Axial load would be carried by the Hinge Pin & barrel under lug.
