I agree, that the trigger works better with the shim.... Perhaps, Lloyd, you would like to comment on this, however?....http://www.network54.com/Forum/275684/message/1366211435/Why+do+people+use+the+mrod+trigger+on+the+disco+instead+of+Challenger-I checked, and the MRod trigger and the Challenger trigger are the same part number, including the drop sear.... AFAIK, the Challenger tube is 7/8" x 0.065" tubing.... Are Crosman just ignoring the potential problem?....Bob