If as you stated your shots are 6' (6" ??) off at times something is drastically wrong. You have a 209 primer with 2-50gr pellets followed by a bullet/sabot combination seated the same eact time? I would swap scopes borrow one if possible or purchase a 39.99 bushnell mount it and try to sight in using new pellets primers and the same bullets as last year. Start at 25 yds with a 3X3 sheet of cardboard. If you can't get the gun to sight-in send it back and explain the problem to TC and the timetable you need it back for. If the gun does sight-in with another scope send the Nikon in for repairs. This is the second problem with triumph/Nikon combinations, maybe a trend starting.