As time goes on, more and more publications are digitised and become freely (and legitimately) available online. Not finding any threads dedicated to listing such resources, here are some, courtesy of the Smithsonian:
The corrugation in African sword blades and other weapons
Hough, Walter
URI:
http://hdl.handle.net/10088/13062
Date: 1889
A study of the boomerang
Eggers, H.
URI:
http://hdl.handle.net/10088/13071
Date: 1889
Distribution and use of slings in pre-Columbian America, with descriptive catalogue of ancient Peruvian slings in the United States National Museum
Means, Philip Ainsworth
URI:
http://hdl.handle.net/10088/15071
Date: 1919
The Long Sword and Scabbard Slide in Asia
Trousdale, William
URI:
http://hdl.handle.net/10088/1332
Date: 1975-05-08
The Collection of Primitive Weapons and Armor of the Philippine Islands in the United States National Museum
Krieger, Herbert W.
URI:
http://hdl.handle.net/10088/10135
Date: 1926