50 and with the rear dog 62 it should be noted that the compression spring 65 biases the rear dog 62 in a counterclockwise direction to cause edge surfaces of the passage not shown to dig into the elongate drive rod 40 for precluding the drive rod 40 from moving in a direction opposite the ejecting direction upon release of the trigger 54 however when it is desired to axially adjust the position of the drive rod 40 manually the finger gripping extension 63 is manually depressed to position the rear dog 62 in a generally vertical orientation to permit free sliding of the drive rod 40 within the passage of the rear dog 62 it should be understood that the arrangement and manner of operation of the rear dog 62 is conventional and does not constitute a limitation on the present invention additionally a return knob 67 located at the proximal end of the elongate drive rod 40 allows the user to withdraw the ejectors 120 from the cartridge assemblies 18 a and 18 b after dispensing of the components 24 25 has been completed or in the event it becomes necessary to replace the ejectors that have become contaminated with dispensing material that has flowed from within the cartridge assemblies back behind the plungers 22 in a manner to be described in detail below although the return knob 67 is illustrated in fig2 as being round it is to be understood that this is not limiting and the.