The degree of difficulty definitley increases exponentially with distance.
From the point of reference of the 308 Win, 500 yards is a relatively easy shot. 1000 yards is a lot more than twice as difficult. Mostly because of the wind, and the art involved.
My 308 155 Scenar load drifts about 15" at 500 (10 mph, f/v), compared to 75" at 1000 yards.
