Pictures of the targets would be helpful. Certain patterns can help pinpoint the problem(s).
Rifles may shoot different brands, or lots within brands better than others. A recent gun magazine found a batch of 180 grain Core-Locts to shoot 2-3" worse than other brands. We've normally found that brand/bullet weight to shoot under 2" at 100 yards.
Try Winchester 150s, Federal Premium 165, Hornady 150 to 180grain. Some rifles shoot best with 168 grain target loads, but they're not good for hunting.
If the rifle still doesn't shoot well, and you are normally a very good shooter off the bench, try a different scope and mounts.
If you're a novice at bench shooting, examine your shooting technique, including having someone load snap-caps within a magazine, to check if you're flinching.