Like the others said it could be excess oil or bore cleaner. Guns are really individual, some of my guns are dead on and some shoot a little off after a barrel clean out. I would say clean it real well, make sure you dry patch it and see if this pattern holds true. As a general rule my final sight in session I don't shoot to many rounds, just make sure it is dandy and leave the bore until after season. I do clean the bore if it is required or real wet to prevent rust or pitting. I clean exterior and lubricate regularly during the season.