The Manual of Small Arms (1945)
If you're interested in learning about the mechanism of firearms, the attached War Department video produced during WWII is surprisingly thorough and instructive. While the terminology and basic concepts were already known to me, the way the information is presented here gave me an even better understanding.
Since they didn't have the kind of graphic design tools we have today for making animated videos, they did a lot of work with hand-carved models that bespeak great craftsmanship.
http://www.youtube.com/watch?v=NZX7X3pJgH8
PART TWO
PART THREE