In 1952, Czechoslovakia adopted a whole new family of small arms, including the vz.52 pistol, vz.52 rifle, and vz.52 light machine gun. The rifle and LMG were both chambered in the Czech 7.62x45mm cartridge, and both would be adapted to the Soviet standard 7.62x39mm a few years later, in 1957. Very shortly thereafter, the Czechs would also introduce a heavier universal machine gun version in 7.62x54mmR under the designation UK vz.59 (universal machine gun model 59).
The UK 59 was basically a scaled up sibling of the vz.52 and vz.52/57 machine guns, although it fed from a belt only, where its smaller predecessors had allowed either belt or magazine feed. It used a pivoting locking block system much like the Walther P38 and Beretta pistols, in conjunction with a long stroke gas piston much like that of the vz.26 light machine gun.
The weapon did not see much interest outside of Czechoslovakia, although it does remain in service in that region in the modernized 7.62x51mm iteration.
Thanks to Marstar for letting me examine and shoot their UK vz.59!