Albert G. Hadcock, Henry A. Bethell, Julian R. J. Jocelyn & Sydney R. Fremantle, 1911 Encyclopædia Britannica, Volume 20… (1911)
“ A stronger material than ordinary carbon gun steel was consequently demanded from the steel-makers, in order to keep the weights of the heavier natures of guns within reasonable limits. The demand was met by the introduction of a gun steel having about 4% of nickel in addition to about 0·4% of carbon. This alloy gives great toughness and endurance under a suitable oil hardening and annealing process, the yielding stress being about 26 tons to 28 tons and the breaking stress from 45 tons to 55 tons per square inch, with an elongation of 16%. ”
