Reddit mentions of Backbone of the Wehrmacht, Vol. II: Sniper Variations of the German K98k Rifle

Karabiner 98k by Karem and Steves is a great resource for K98k snipers, particularly Volume IIa. There are currently 3 volumes, Volume 1 covers pre-war (banner model, standard modell, etc) to 1938 rifles at Mauser-Oberndorf, JP Sauer, Mauser-Borsigwalde, Ermawerke, Berlin Lubecker, and BSW. Volume 2 covers wartime production, and Volume 3 covers the Kriegsmodell. 2A specifically has a lot of info regarding sniper rifle development at Mauser-Oberndorf, specifically the ZF-39 (low and high turret), the ZF-41, and the Jung Prismatic Optics prototypes. The 3 book set is an excellent resource for the history and engineering of the German K98k. The only downside to the books is that they are pretty pricey, at $345 for the 4 book set (Volume 2 is so large that they had to split it into 2 volumes).
Link: http://www.thirdpartypress.com/category-s/1632.htm
The only other "WW2 German Sniper" book I know about is Backbone of the Wehrmacht Vol 2.
Link: https://www.amazon.com/Backbone-Wehrmacht-Vol-II-Variations/dp/0889352224
I personally do not own volume 2 (I own volume 1), but it seems to be a decent source on the rifles.