[4V50 Gary]

Distance estimation was formerly taught in Confederate General Patrick Cleburne's division in The Army of Tennessee. Cleburne based his training on a British musketry manual. Confederate General Cadmus Wilcos was also thought to have authored a booklet which was distributed to the sharpshooter battalions in the Army of Northern Virginia. It too was based on the lessons in the British handbooks. I know Confederate Henry Heth did some research, taught it in the antebellum era and even wrote a booklet which someone else plagiarized before the war, but I found no evidence that he instructed his division during the war. (Heth's infantry started the battle of Gettysburg when they fought with Buford's troopers).

Like Hal said, you looked at something (like a wagon or artillery piece) and then paced off the distance. You told the officer who wrote it down and called the next man to give his estimate. Records were kept and those who could not get the knack were washed out of the sharpshooter battalions (in the Army of Northern Virginia). In about a week's time the men got pretty good at this.

Artillery men on both sides became very good at range estimation and they had to if they were to adjust the fuse correctly. Overestimate and your shell explodes past the target. Underestimate and your shell explodes before it reaches the target. Gibbon's treatise on artillery covers range estimation too.

There were also mechanical devices called stadia that could be helpful. You held the stadia a fixed distance (a length of string) held beneath the eye socket and measuring the height of the man (average soldier was 5'8") or horseman against the distance marks on the stadia. Read the distance on the stadia and you've got your estimate. There were antebellum optical devices that also had stadia wires in them that could be used for range finding. So the concept of the mil dot is not new. However, these would have to be privately purchased and I haven't read anything proving any officer on either side using one.

In my research I found no evidence that this was done by Union infantry.

Go to the National Battlefield Park and ask to use their library. Most Civil War National Battlefield Parks have my book (Sharpshooters (1750-1900): The Men, Their Guns, Their Story) and the subject is covered extensively in Chapter 7.