The M14 rifle was the result of the US Armys search for a replacement for the venerable M1 Rifle, introduced into service officially in 1957 the rifle served until it was replaced, in turn, by the M16 in the late 1960s (phased in during the Vietnam war).
A semi automatic, magazine fed rifle chambered for 7.62xx51mm the M14 is essentially an improved M1. Just over 1,000,000 M14s were produced and as designed the rifle was capable of use as a personal weapon and as a squad automatic weapon (this involved the installation and use of a fire selector switch, although it was determined that the M14 was not uniquely suited to this role).
The SKS rifle was designed by Sergei Gavrilovich Simonov, based in part on his earlier work on the PTRS anti-tank rifle.