Are you referrring to the new Hornady FPB's....they are 350gr.?
If so, I and many others have been getting good accuracy with them. My experience with them has been limited to my Omega using 100-110gr. charges of Blackhorn 209 powder.
Is your powder old....from last year? Did you try to work up your most accurate load at 50yds. before going to 100? Make sure your scope base and rings are tight. If you have access to a good bore sighter, you could check the zero of your scope and see if it changes. Then you know it's either you scope or mounts.