K bullet

Also: Patrone SmK (Spitzgeschoss mit Kern) 8×57mm IS

The K bullet is a 7.92×57mm (8×57mm IS) armor-piercing bullet which has a tool steel core and which was designed to be fired from a standard Mauser rifle. It was used by the German infantry against the first British tanks in World War I. The K bullet had a probability of approximately one-third to penetrate armor 12–13 mm thick up to a distance of 100 meters.

The K round was in use by the battle of Messines Ridge in June 1917 which was the first use by the British of the Mark IV tank which had more armour and was resistant.

Variants
The Germans made several versions of the K bullet during World War I and World War II, including:

During the interwar period, Poland produced a copy of S.m.K. bullet designated as P bullet (przeciwpancerny) and own armour piercing bullet with a tracer, designated PS (przeciwpancerny smugowy).