I thought I would try to clarify the setup of the Screw Grip on this Heliduplex gun. The screw grip actually bears on the top on the rib extension and on the bottom on the modified rear locking lug which sits at a higher position than if a Purdey underbolt locked it. I’ve not seen a similar arrangement on any other gun I’ve run across. It is an immensely strong lockup. I have two original V-C catalogs from the 30’s that show it as their top offering.