Mauser 416,

In my opinion, the true circle bearing surface is far superior to the flat surface, for two distinct reasons.

The first one is very easy to understand and visualize: Because of the very nature of the design using the flat surface, the two mating surfaces cannot come in contact with each other until the breech is fully closed. The slightest amount of dirt on the breech-face or the water-table, or an oversized shell, even if by only a couple of thousands of an inch will prevent the two surfaces from mating. This of course will put the entire load on the hinge pin.

The same situation would have no such effect with the radial bearing surface (the circle), since the two surfaces are fully mated during the entire opening range.

The second reason is a bit more complicated and difficult to explain without detailed drawings showing the vector lines of the forces in effect. But, I’ll try:

At the time of firing, the fore and aft force acting against the barrel and the breech-face, is not entirely horizontal. On both systems, there is an upward force trying to swing open the breech. This upward force is due to the fact that the hinge pin is below the centerline of the barrels; the lower the hinge pin, the higher the upward force. This force can be easily calculated with the use of a vector drawing.

On the flat surface system, we have an additional force trying to open the action: the necessarily angled surfaces act as an inclined plane, just like a set of adjustable parallels; as they are squeezed together, they try to slide. This again can be demonstrated and calculated with the use of vectors.

Max