Yes, they did kill folks out to 800-1000 yards during the Civil War. There was a federal general killed at Cold Harbor while haranguing the troops with: "They could not hit an elephant at this range." A bullet struck him between theeyes.

Those rifles usually weighed in excess of 15 pounds and had huge barrels with false muzzles for loading. A scoped Whitworth sniper rifle costover $1,000-big money for that time.