The piston pin of the Mercedes is of chrome nickel steel, and is retained in the piston by means of a set screw and cotter pin.
"A History of Aeronautics" by E. Charles Vivian
Chrome-vanadium steels have been claimed, by many steel manufacturers and users, to be preferable to nickel-chrome steels.
"The Working of Steel" by Fred H. Colvin
The material of which these guns are made is nickel chrome gun steel.
"Marvels of Scientific Invention" by Thomas W. Corbin