Forces required to keep the barrels on face is something that I have been interested in for some time. If one looks at the forces involved when a break-down gun is fired, the following are obvious: 1. Back thrust of the cartridge case upon the standing breech(+) 2. Forward thrust resulting from the projectile engaging rifling, and then friction whilst traveling down the barrel(+) 3. Friction of the case head upon the standing breech (-). (N.B.: The (+) symbols indicate a force that tends to open the gun. The (-) symbol indicates a force that tends to retard opening the gun.)

The pivot point is at the cross-pin, and that is usually offset from the bore axis; therefore there is a force-couple, in effect a rotational force, centered around the cross-pin. If the cross-pin was coincident with the bore axis, then the effective force-couple would be zero, and the action would tend to remain closed, even in the absence of a positive lock. That being said, the action of recoil against a pliant surface, i.e., the common human shoulder, would tend to break the joint and the gun would open in actual practice - if there were no positive lock.

I like your ideas; however, I wonder if the Bissel rising bite is any more effective than a properly fitted Greener cross-bolt. Is there more mechanical advantage with the Bissel due to the locking surface being somewhat further removed from the pivot point?