I don't have time to go looking for first hand account right now... will try later in the week.
But I do suggest books like: (They do a much better job at explaining the point.)
Earl J. Hess:
"Civil war infantry tactics"
"The rifle musket in civil war combat"
Nosworthy:
"The Bloody Crucible of Courage: fighting methods and combat experiences of the Civil war"
Paddy Griffith:
"Battle Tactics of the Civil War"
The problem with firing at long range it, as mentioned the low velocity.
The result is that if you with a springfield set the sights at 300 yard and fire, but the enemy was only 250 yards away, the round will go over his head.
Raserende-skudbane-nr1.jpg
The result is that hitting at 300 yard require a good marksman that can judge the distance correctly. And there was simply no organized system used for teaching this to the soldiers.
(Cleburne who had experience with the british system did institute training in his division, but this was an exception)
Griffith calculated an average first volley of around 140 yards.
Page XII (preface) in "civil war infantry tactics"
Hood before the Atlanta campaign: "
Firing on the enemy at long range should never be permitted, since its lack of effectiveness often gives encouragement instead of causing demoralization, as a well-directed fire at short range is certain to do."
(...)
and Benjamin F. Cheatham recalled that on the battlefield of Franklin, where the Army of Tennessee attacked across a broad, open area, bodies of his men lay as fare away from the federals as 400yards, but the great majority of dead and wounded lay within 50 yards of the defenders.
Also remember that for half the war smoothbore muskets was common in the ranks of both armies.
But maybe we should take this to another topic...