K bullet
Also: Patrone SmK 8×57mm IS
The K bullet is a 7.92×57mm armor-piercing bullet with a tool steel core 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 and on the Panzerkampfwagen I. On average the K bullet has a one out of three chance to penetrate armor 12–13 mm thick at a range of up to 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:| Designation | Full Name | Description |
| S.m.K. | Spitzgeschoss mit Kern | Standard steel core armour piercing bullet. It had a red rim around the primer, on case base. |
| S.m.K.H. | Spitzgeschoss mit Kern, Hart | Replaced the tool steel core with a tungsten carbide core. It had a red case base including primer, from 1939: red primer only. |
| S.m.K. L'spur | Spitzgeschoss mit Kern, Leuchtspur | Has a shorter steel core, and includes a tracer composition. May include color designation such as gelb, German for "yellow". It had a red rim around primer and black bullet tip. |
| S.m.K. Ub.m.Zerl. | Spitzgeschoss mit Kern Übungsmunition mit Zerleger | A very rare practice bullet which self-destructs after a certain distance. |
During the interwar period, Poland produced a copy of S.m.K. bullet designated as P bullet and own armour piercing bullet with a tracer, designated PS.