So I am new to longer range shooting and need a little help. I am trying to use the phone apps Shooter/iSnipe to help me get on target. I have entered all the data that I believe to be accurate and both put me about 1 MOA lower than actual at 500 yards. How can I take the actual working numbers and extend that out to longer ranges for more accurate dope. I have a 1000 yard target, but it's fairly grassy and misses are hard to see. Maybe I should put a 4X8 sheet of plywood up to help get me zeroed in.