IMHO an action invented before WW1 may not be called "new-fangled" exactly. Franz Jaeger of Suhl patented his "break-open block action" quite early, German DRPatent Nr. 209113 of 1909 and US patent 928608 of 1908. What some of you called a "breech cover" is in fact an essential part of the lockup, a top extension of the barrels or, in case of the Blaser, of the monoblock. The moveable breechblock, containing the strikers, is L-Shaped. On closing such a gun the block slides up behind the breechends at a right angle, just like a falling block. The lower end of the L hooks over the rear barrel lump. The ridge on top of the block engages a groove in the underside of the barrel extension. The block has to be movable to allow the gun to break open around the hinge pin, but when closed, it is locked directly to the barrels. In fact, you may disassemble barrel and breechblock from such a gun, load the barrels, slip on the breechblock, keep it in place by a rubber band or a piece of tape and fire the barrel by hitting the firing pin with some hammer. All pressure is contained within barrel and breechblock, the action body merely keeps everything, lock, stock and barrel together and transfers recoil to your shoulder.
I do not defend Baser guns, I don't like them at all. In fact, someone once suspected me of catching pimples from touching a Blaser gun, but I criticize style and workmanship, not old Franz Jaeger's basic action design. But on a double rifle I deem it unnecessary. Simply don't use rimless, belted or high-pressure "modern" cartridges in a double. Proper dr cartridges are rimmed and comparatively low pressure, simply as old-fashioned as a double. Then a conventional break-open action with a long water table, generously designed double underbolting and some sort of third bite / top fastener is sufficient. But too many hunters believe now that they cannot kill anything without a load making at least 3000 fps. They are the buyers of Blaser's contraptions.