"Shock Troops of the Confederacy – The Sharpshooter Battalions of the Army of Northern Virginia" by Fred L. Ray. Published in 2006. The back cover has a web address cssharpshooters.com – haven't checked it to see what is there. Rather than give my opinion (and who cares about that?), I'll just quote from the back cover:
Robert Krick: "Tells the story of the Army of NV sharpshooter battalions here for the first time, based on a very strong range of primary material, including some thirty manuscript collections, scores of arcane articles and narratives, and numerous obscure contemporary Southern newspapers."
Jeffry Wert: "A most welcome and long overdue study of a neglected subject – the sharpshooter units of Lee's renowned ANV. He recounts their story in detail and with authority."
William C. Davis: Provides our first and most detailed to date look at the development of the concept and practice of sharpshooting, its goals, the men who became killers, and their impact on the course of battle"
Joseph Bilby: "Without a doubt the most significant small unit tactical analysis of the ANV ever written".
Basically the book follows the sharpshooter experimentation from the start of the war and details their expansion and development. From the first battalion in Rodes brigade in early 1863, to one in each brigade of his division later, the concept went to direction of a battalion per brigade in 1864. The book looks at the development of the battalions, their weapons, and tactical use.
Brilliant book. My opinion.