just to cover some basics. Is the rail tight on the reciever? Are the rings torqued evenly on the rail, Are the ring caps tight? Is the eye relief set properly? is the image viewed through the scope clear, no shadow around the edges? It is strange that the rifle is shooting higher at 300 than at 100. If I had a problem like this, I would be hunting for my glasses and making sure everything was right and tight
Hundreds of years from now, it will not matter what my bank account was, the sort of house I lived in, or the kind of car I drove... But the world may be different because I did something so bafflingly crazy that my ruins become a tourist attraction.