I am with Jack and DAA on the mirage thing. I dont' care what they say, shooting groups in high mirage is next to impossible, even at 100 yards. You have no pin-point spot on the target to shoot when it seems to be moving like a jumpin-bean! Also, head and tail winds do some pretty strange things when you add distance.
DAA has another good point. You have to shoot your loads and rife at the distances of the match in practice and at the match. Just like sniping, you have to write down every shot,account where it goes, and all the weather effects,good or bad, every day. When preparing for a match such as this, I would have the match set-up exactly on my range as there but the targets would be circles drawn to exact ballon spec's with some sort of aiming point in the center. This way I will have exact point of impacts for all shots to log. I will shoot it everyday rain or shine and note every shot
Dead on at 7:00am will not be dead on at noon and will change during the day as it heats up and cools down. As to how much it effects your rifle and loads will have to be figured out by you. Points of impact change with heat and cold. General rule of thumb is less humidity higher it shoots and higher humidity bullet drops more at long range. Remember, nothing is exact or the same. Only close if you are lucky!
The last thing and foremost on my mind is, "Does your scope track properly everytime." I have tested every target model on the market for the last 20 years and there are very FEW that can or do! This would be the first thing I would check if you are an experience shooter. Do a simple 10" square test on it at 100 yards at least a couple of time and 200 too. If it can pass this, then welcome to the real world of long range shooting where the difference between the men and the boys is knowledge and luck!! Or at least that is what the old'timers always told me!! I am fortunate enough to know some of the best shooter in the world and they still have trouble too!! Good Luck!!! Sorry can't be of more help. This is one of those impossible questions we all want to know the answer too.
