My rifle required that one pull back on the rear trigger to get it to set, harder than one would imagine. In regards to the screw between the two triggers back it out a couple of turns, set the rear trigger and while leaving it set slowely screw in the screw while watching the front trigger move back towards the rear trigger. When the trigger lets off back the front screw out about a 1/4 turn and makes sure it sets reliably if not back it out another 1/8 to a 1/4 turn. 

JLouis

There is also a flat spring pushing down on the back of the sear block in the same basic location that is also a function for setting the trigger. I have had to bend that spring down in the last to provide more downward force on the back of the block. I have also seen it slide of the block completly and there would then be no way for the back trigger to set. Sometimes you can sort out which problem it is by pushing forward on the back of the front trigger and then try setting the back.