An interesting tidbit is that while the general impression that Confederate soldiers were better shots in general than Union troops is true, when it came to dedicated sharpshooting the north had the edge in both organization and ability. Some union officers, the well-known Hiram Birden among them, actively sought and recruited professional long range shooters, and worked to have them armed and organized to best utilize their skills.
And this marksmanship selection of "country boys" continued into later wars because the military knew the city boys did not grow up with a rifle and pistol in their rooms and learn at an early age how to use them proficiently.
So the basic skills of stalking and hunting your prey which every sniper needs is usually well taught to the country boy. Including the patience to sit in a hide for hours on end for that prey to make a mistake, is already there as well.