Coach4christ......I'm almost 99.5% certain that there is not an issue with your scope. I left that .5% open because scopes are mechanical and mechanical things do break. But my thought process is that when we sell the quantity of scopes that we sell and only see roughly 3-4 scopes per week back for warranty repair as a result of the intensive QC process that every scope receives prior to going out the door, its easy for me to question whether the scope is an issue or not. Your scope would have not been allowed to leave the factory if their was any backlash or tracking issues. The QC process that our scopes go through are the most rigorous in the industry. And its not a batch test. Each and every scope is tested prior to receiving the QC label.
I'm thinking you may be dealing more with atmospherics or hot chamber temps causing a velocity increase that is changing your point of impact. Things of which can be very repeatable and must be known variables when considering predictive solutions for long range shooting. My 300 Win Mag will shoot exactly 1moa high after I fire 20 rounds through it in less than 5 minutes time. What is your DA when you start shooting and what is your DA when you return to Zero?
I'm also curious as to how you set your ZeroStop just to work through and eliminate some variables? Did you zero the rifle at 100 yards and then slip the scale back to zero or did you adjust the ZeroStop as per the instructions?
Are the opposing turret cap screws tight enough so that the turret cap is not slipping? Are the 4 screws atop the ZeroStop clutch assembly tightened to 4in. lbs each?
Since I'm rather positive that it is not an issue with the scope, I'm just trying to work through other possibilities.
I followed the instructions to the T. 4 in. lbs for the screws on top. I tried to feel for slippage, but didn't feel any. I hear what you are saying about barrel temp and all, but if that were the case, the rifle wouldn't be zeroed the next time I shoot it. When I start my shooting sessions, my rifle is dead on every time.
For example, A week ago I had this problem. I rezeroed my rifle and went home. Here is a pic if my first 5 round group. If it were barrel heat, they would not have been dead on, they would have been high.
http://i897.photobucket.com/albums/ac172/coach4christ/5r.jpg