It appears that this has been a very active thread while I was at work.For the record,I would never attempt a 600 yard shot at any big game animal.Under perfect conditions,500 yards would be my absolute limit,and if there is any crosswind,or a solid rest is not available,my limit is adjusted to a much more conservative distance.I have shot 3" to 4" groups at 500 yards from a benchrest with my hunting gear,but in the mountains,there is almost always wind ,and the shots are often at angles that complicate range estimation,even with a laser rangefinder.