From Greener's 9th Ed., page 187, I can't say for sure that the Deeley ejector gun required the front screw and so it may very well have been Perkes which was "actuated by a lifting lever, pivoted near the hinge-pin, pressing upon the extractor leg as the gun opens." And from the pic, the screw could be the source of the pivot but I have seen the screw as a stabilizer for the kicker.

Kind Regards,

Raimey
rse