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Here are the rivets all the way down to the very last one accessible to the rivet gun.  
      The second picture above shows the positioning of the bucking bar.  It is sitting on a steel plate and the rivet factory head is resting on the top of the bucking bar.  This is just how it should be set up for back riveting with the Sonex Rivet Tool.  Just strike the top of the rivet shank about three times and the rivet is set.

      I replace the Sonex Rivet Tool with a 3x rivet gun borrowed from my RV building friends and use the back set tool.  This back set tool has a collar that helps keep the gun from wandering off the rivet shank. The surface inside the collar is flat like a flush set tool.

      All of these rivets on the outer spar are the same and the pull time with my metronome is  a – ONE AND TWO – count at 120 beats per minute.  That’s .75 seconds, with 90psi and a full pull on the trigger. The set rivets next to the tool show the result.