Book Of The Rifle
Jim Carmichel, best known for being the Shooting Editor at Outdoor Life, was also a top notch competition shooter in High Power, Long Range and Benchrest disciplines. Now retired, he was one of the few truly authoritative gun writers that combined proven, winning shooting skill with a well studied history combined with an approachable writing style.
The Book of the Rifle is his masterwork and remains possibly the best single text on the subject. It is an incredibly complete look at the rifle, its history, development and application. Though primarily focused on the hunter and sportsman, it covers some aspects of military application and competition.
The history of competition shooting is incredibly important to both firearms and marksmanship development and I wish Carmichel spent some more time on it, but I suspect this made his book more approachable to typical hunters and other gun owners.
The section on marksmanship was shorter than I would have liked, especially considering Carmichel had the chops to elucidate further, but his approach was both novel and useful.
If you ever wondered how rifle work, I mean how they REALLY work, and why, this is the book to get.