I'm far from knowing much about Beretta triggers, from the picture , the pendulum moves back the block moves back and allows the block that goes under the sear tails to move side to side. If both hammers are cocked , and you move the barrel selector back and forth it kind of does the same thing without the pendulum moving. Pull the trigger, then pull back on the pendulum. That should shift the block over. Whether that makes sense or not , that;s my story and I'm stickin' to it!