Try:
"The
British Sniper" 1915-1983, by
Ian Skennerton, which may be a bit hard to find; check out the book dealers at gun shows. LOTS of tech stuff, and a few "eye-witness" accounts in there.
The two aforementioned books from the pen of "our very own"
Peter Laidler are essentials for technical stuff.
The "Snipers to the Reich" book is somewhat less about the "nuts and bolts". I'm only guessing, but probably not a lot of snipers would seem likely to be writing "ripping yarns" about what they saw through their scopes as they plied their trade.
There is also a different tale, one from an American who joined the
Canadian Army during WW1. "A Rifleman Went to War", by Herbert W. McBride.
From "the other side", there's:
"Sniper on the Eastern Front: The Memoirs of Sepp Allerberger, Knight’s Cross", by Albrecht Wacker. I haven't read that one yet, just had it recommended to me.
I'm fairly confidant the Russians have published some interesting books, as well.