Ross, both lugs are actuated by the top lever. The smaller lug closest to the breech is fixed, the larger lug toward the muzzle has screws in the bottom, which you can see in the 4th photo you posted for me. In the 2nd picture, the two pieces of metal in the square lug holes retract toward the face when the lever is pushed, thus disengaging both lugs and the gun opens. Does that help?