I have just started working on long range shooting and have problems with my calculations. I can think of several reasons why they would be off and wonder what's the best order for the process of elimination. The problem has happened with two different rifles and I am usually off .5 to 2 MOA always high. Shooting from 400 to 500 yards. Today I was off about 2moa at 470 yards. I have used online calculators and charts in my reloading books, which both come out the same. I shoot on flat ground, the velocities I use to calculate are averaged over many rounds and conditions, some taken the same day. The optics are Leupold and Vortex, but I have never verified them. Should this be done at 100yds? I have no rangefinder, how reliable is Google earth? I'm using very easy to see landmarks, and think I'm getting good measurements on the program. I have also used measuring wheels that you walk behind, GPS and other things. I'm about 800' elevation shooting at around 70 degrees F, little to no wind. Possible problems I can think of: The bullet is traveling faster than I think The range is shorter than I think The adjustments on the optics are not accurate My shooting form Any more Ideas?