Dunlop's book is "Lee's Sharpshooters or Forefront of Battle" and a good hardback is published by Morningside House Press in Dayton, Ohio.
Another good book is Charles Stevens' "Berdan's Sharpshooters in the Army of the Potomac." Also published by Morningside.
Benson's Confederate Scout-Sharpshooter (alternatively called Confederate Scout-Sniper) is a must read and is perhaps the singularly the best account by an individual sharpshooter on the Confederate side.
William Green's book "Letters of a Sharpshooter" is OK, but I really didn't find much useful or interesting anecdotes from it.
Wyman White (2nd USSS) is my favorite book by an individual Union sharpshooter. It's a must read and is comparable to Benson.
Katcher's book is a so-so "peanut butter" book which is OK, but there are some inaccuracies in it.
William B. Edwards book is still one of the best. Published in 1962, it is well researched and has good photos. BTW, I met the man once.
Roy Marcot's book "Civil War Chief of Sharpshooters Hiram Berdan" is a very well researched book on Berdan, his men and to some extent the guns. Hard to find though.
Go to
http://www.thehighroad.org and drop into the blackpowder forum. Look for a thread entitled "Bedtime Stories or Sharpshooter Tales" for a disjointed presentation of some vignettes/snippets.
BTW, I saw that photo of the telescope rifle at Gettysburg but there's nothing in the provenance (that I saw) that shows it was used at that battle. There is certainly nothing proving it was captured at Devil's Den.
Concerning the Bleak House in Knoxville, I'm very well acquainted with it and was under the impression that the soldiers were South Carolinians. The distance was more like 750 yards from the tower to where Gen. Sanders was shot. Love to see your article and can you provide the link?
Shane - where'd you read that story about Grant from? I don't recall that in his memoirs or Porter's Campaigning with Grant.