i had the rifle out at the range this past week and i didnt notice anymore shift from my last session. i still do not know what caused the shift in the first place. i think i will just re zero my scope and not worry about it till i can get someone that knows a little more than me to look at it. thanks macgrumpy those are some very good ideas on making sure the holes arent drilled off center. i think i will try that the next time i have the scope off. i dont think the holes are drilled off center but it doesnt hurt to make sure. thanks again for all the good ideas and happy shooting.