I noticed my pellet probe has to lift itself into alignment a few thousandths to the barrel as it contacts the breach face. That can't be good for the O-ring or initial pellet alignment. Not wanting to tear it apart and see what the fault is, I simply put a a Delrin guide below the probe block. Pinched it in alignment with a couple of machine screws with plastic washers, threaded into the Delrin block . Smooth as can be now 
https://www.youtube.com/watch?v=zGvam8_E9Ls
https://www.youtube.com/watch?v=zGvam8_E9Ls