Whenever I go shooting I always start at 100 yards to check my zero. It usually take 1/4 Moa or so in some direction to get it on. The atmospherics are the same plus or minus 10 degrees or so an this is non clean cold bore shooting. I will do nothing to my rifle when I am done shooting, go back next weekend and it is off again. I handle it carefully and it is a leupold mark 4 with badger rings/ base. So I don't think anything is shifting on me. I make sure there is no parallax before I start. Also using the same lot of components. I have noticed it with me with other rifles as well as other people going through the same thing. Anyone else have this problem? What can cause this?