We remain OT, but relevant to the discussion
Chapter 15 of
Shotgun Technicana by McIntosh and Trevallion discusses Top Fasteners and specifically the Alexander Brown patent, and the almost identical Ansley Fox patent.
"The most basic principle in fastening any hinge is that the farther the fastener is from the hinge itself, the greater the mechanical advantage. Thats why door latches are placed where they are. In a gun, the action bar and breech face form two sides of a right triangle, so that the top or the breech face is farther from the hinge pin, in straight-line distance, than the bottom. In a side-by-side gun theres an additional advantage in that a top fastener is a bit more efficient in overcoming the effects of barrel flip-for the gun, if not for the shooter. With a top fastener, the barrels still flip downward on firing, but the action bar flexes less, and the fastener keeps the top of the barrels from pulling away from the breech face."
"The most interesting of the American top fasteners is the L.C. Smiths patented by Alexander Brown in 1883. Where all the others used either Greeners transverse bolt, some sort of flat bolt or hook on the front end of the top lever, or both, Brown designed his bolt as a steel cylinder that turns on a horizontal axis. A slot filed into the cylinder forms the actual hook, which fits into a slot in the rib extension. The cylinder also engages a lip at the rear of the extension as a secondary bite. L.C. Smith described this arrangement as a double cross-bolt, although double rotary bolt would be more accurate."
More here
http://www.lcsmith.org/faq/rotarylocking.html 
