If you took a line from the center of the hinge pin to the juncture of the watertable & standing breech then a line perpendicular to this line would be tangent to the circle of rotation, thus the gun would open & close if cut to this angle.
Just grabbing one gun at random & taking a rough scale measurement I got about 2Ľ from the center of the hinge to the standing breech & about a 7/16" from from the water table to the hinge center. Using trig to find the angle from the hinge center to the base of the standing breech gives about 11°. While this much forward angle to the standing breech would certainly not be desirable the gun Would Open even if perfectly jointed.
