Try one thing at a time, if you have a known good scope replace the old one and find out. In some of the guns i have checked out it has been the scope. I replace with a known quality scope and groups shrink. I have found a bad leupold and weaver scope by doing this. If I was not such an honest guy I would have gotten 2 guns for dirt cheap, the one bought a leupold and is very happy. the other as of now is sending his back to leupold for the second time, not quit happy with leupold right now.