|Each colored segment equals 1,000 yards. The vector illustrated here is drawn|
on the Cope/Carman Map (1908 edition) for 9:00 hr. and shows range
vectors for Taft's battery of four 20lb Parrotts set at 15 degrees elevation.
At 15 degree elevation, Federal Parrotts could hit most anything within 4,400 yards. This capability is sometimes forgotten and in many sources, the "maximum range" for the 20 pounders is listed as less than 2,000 yards. This is a correct figure for a five degree elevation but ten more degrees made all the difference for many on the field on September 17. The fields adjoining the West Woods were no exception.
From Ezra A. Carman's manuscript:
"At daybreak [on September 17] an artillery duel began across Jackson's front between Doubleday's and Stuart's guns, and soon after daybreak a stream of round shot and shell came from Matthews' and Thompson's batteries on the Miller farm; and from the heavy guns beyond the Antietam came a fire which enfiladed Jackson's Division and took it in reverse. Poague's and Brockenbrough's guns replied to the guns on the right front, but Brockenbrough was soon ordered to retire through the West Woods." 
"From Taft's, von Kleiser's, and Weed's positions one could look to the right, through the open space between the East and West Woods, and see Hood's men as they advanced to meet Hooker, late in the day, and their guns were brought to bear upon them, as also, upon Jackson's men as they took position near the Dunkard Church, about sunset [on September 16].
"From the bluff north of the Boonsboro road the gunners could look down the Sunken road, and it appeared but a stone's throw to Piper's cornfield in and around which were the men of Rodes' Brigade.
There were very few points of the Confederate line that these batteries could not reach, and on many they had an enfilade and reverse fire. "
There were 22 twenty pounders in the Federal arsenal. 
 Ezra A. Carman, The Maryland Campaign of September 1862, Vol. II: Antietam. Thomas G. Clemens, ed. (California: Savas Beatie, 2012), p. 68. Emphasis added.
 Ibid., pp. 22-23. Emphasis added.
 Curt Johnson and Richard C. Anderson, Jr., Artillery Hell: The Employment of Artillery at Antietam (College Station, Texas A&M University Press, 1995), page 129;