Sporter contour, yes, mcmillan. I dont do it at 100 (vertical string) so signs point to shooter error I would blame input bias because I sometimes find myself cheating by trying to sneak a little closer to the holes I see, but you cant see those tiny holes at 600 with my equipment. I think I might have been snuggling up to the gun a little more in an attempt to hold the muzzle down so I could watch the impact dust cloud.