In the original M77 the heavy barreled swift's seemed charmed. All shot well and some were absolutley scarey.. If it's shoting that far apart and shanges between sessions and the scope hasn't loosened, the scope is likely bad. If iy shoots 2 groups, it likely got bedding problems or problems in the erector tube,,scope problems again.. Try it with a scope that is knon to be OK,, and check to be sure all is tight..