For those interested, I would refer you to Don Zutz’s book, “The Double Shotgun” where in Chapter 7 he goes into detail about the three key stresses placed on a double when fired. These are axial force down the bore, radial force which is around the hinge pin and bending force which goes from the breech face through the hinge pin. He specifically says the “radial force pertains to the rotational movement of the barrel assembly around the hinge or knukle pin of a drop-barrel shotgun.” He further says that the “single most important job of a double’s bolting system is minimizing the bending force’s impact on the action frame.” In all cases, the force of this bending goes through the hinge pin, hence the issue of high pressure for short duration. A similar explanation is also in "American Shotgun Design and Performance" by Wallack.
On a Win 21, the water table is unusually long and reduces the bending force by changing the lever arm that is exerted on the action which is why this is one of the strongest double actions. It probably also explains why this can be held closed.
Thanks
Z
