I love old military firearms manuals. Sometimes you can find some real treasures inside the books. A few years ago I bought, (from Amazon I believe) a SMALL ARMS FIRING MANUEL - 1913, in excellent shape. I believe it was a pocket manual issued to the troops. Its about 4 X 6 inches, 249 pages. With fold outs of tables and diagrams.
This book was a great find, but to add gravy, inside the book was a hand written letter from the sister of the soldier who carried the book to her son who was just joining the army.
The letter was about the history of the soldier who carried the manual. Telling of his adventures in the Yukon Gold Rush, baking and furnishing bread to victims of the San Francisco Earth quake. His service during the Spanish American War, being commissioned to serve in WWI, where he was wounded and disabled.
Another find was a book I found at a garage sale in Indiana. Though not a military manual is related.
THE WHY, WHEN AND WHERE OF THE EUROPEON CONFLICT- 1919, a history of the US evolvement. Paid $7 for the book. I was a few months later when I really started going through the book and found, smashed between its pages a dried orginal poppy from Flanders Field.
Why family members let this stuff go is beyond me, but they do and I take advantage of their loss.