The patent specifies link C
. So if it part of the patent there is no stretching.
The double gun-barrel and joining means as described, consisting of the barrels b1, b2, breechpiece a, a1, a2,strips d e, and link c, substantially as set forth.
Certainly they kept changing the methods after Henri Pieper's death. If they modified the patent when their methods changed as would be usual, I can not tell.
Neither his patent nor the documents he submitted in Paris specify how the tubes are held in place.
Here are two images from a Société Anonyme Anciens Pieper Establissments (AEP) 1911 catalog
Long after his death, the company is still producing the Diana, the 1881 patent, monobloc
As well as this demibloc model.
I own a Diana (c 1883), a Modified Diana (c 1895), a later demibloc (1925) and a very late (1947) demibloc. When he was alive, Henri Pieper was a bit of a tinker. He was constantly experimenting with means to cut out steps and increase the automation of his factory.