If when you fire the backblock pushes the cocking rod all the way back but the the cocking rod goes all the way back in again then its a case that the lug on the hammer isnt catching on the sear.. To lower the lug you need to take the bolt out and put an allen key down the hole in the top of the marker half way between the feedneck and backblock, it should go through the top tube and rest on the hammer, is you slowly pull the cocking rod back while applying a little preasure to the allen key youll feel it drop down into the lug, clockwise screw the lug downward dont go to far or it wont release when you fire