Being virtually strictly a SxS man I am not really familiar with how the Benelli operates. That said however all mechanisms with which I am familiar which operate by inertia have the inertia parts aligned axially with the bore or very nearly so. This is true of single trigger inertia blocks as well as the bolts of recoil operated guns, of which I do have several, just not shotguns. The rotary bolt on a Smith, Fox or Ithaca is set in line with the bores "But" it rotates at right angle to that line. There are no inertial forces acting in that direction.
The inertia on a sliding underbolt would actually tend to tighten it upon recoil starting, but would transfer to opening as the guns recoil was stopped by the shooter.
Greener was of course extolling the virtues of his Cross Bolt in his statement. It must be fully realized the "Back thrust" of the firing is directly in line with the bore axis. Since the hinge f a normal double is below the barrel line then some of this force is transferred to an opening action, though not as great as the direct force placed upon the standing breech.
"IF" of course there were no case head thrust there would be no need for any bolting at all except just enough to keep the gun closed for firing. The action could as well be made of a piece of pine. I think a bit of thinking & common sense will show this is not the case.
Greener did further show by firing his gun with the cross bolt made so as to be placed in position or removed by hand that his action was strong enough to hold all normal loads without the cross bolt. he did this by placing a non elastic strip across the gap securely held on both sides. upon increasing to heavier than normal loads he began to break this strip without the cross bolt but with it in place could load still heavier & did no succeed in breaking it with any load the gun would otherwise stand.
