All Department of Defense publications are public domain. They were assembled at tax payer expense and available copyright free.

I’ve seen a number of places and people offering military manuals for sale. While this is legal (any work in the Public Domain can be used by anyone at will) it’s silly, especially because they can be copied and freely given away. Military manuals have been distributed electronically, typically as PDFs, for at least a decade.

Some examples:

US Marine Corps


United States Marine Corps rifle and pistol marksmanship training, 1935
https://archive.org/details/unitedstate00unit

MCRP 3-01A Rifle Marksmanship
https://archive.org/details/MCRP3-01A

MCRP 3-01B Pistol Marksmanship
https://archive.org/details/MCRP3-01B

Army

FM 3-22.9c1 Rifle Marksmanship M16-/M4-Series Weapons
https://archive.org/details/FM3-22x9c1

FM 3-23.35 Combat Training with Pistols, M9 and M11
https://archive.org/details/milmanual-fm-3-23.35-combat-training-with-pistols-m9-and-m11

Military manuals suffer from “encyclopedia error” – where new editions are typically created by pasting together old editions, not through scholarship and new research – and represent a novice level of skill and understanding. Still, they cover fundamentals and those are always important.