The 6.5×54mm Mannlicher–Schönauer also known as 6.5×54 Mannlicher–Schönauer Greek or simply 6.5 Greek is a 6.5 mm (.264" cal.) rimless rifle cartridge used in the Mannlicher–Schönauer rifle. It is the direct descendant of the 6.5×53mmR rimmed cartridge from the 1891 Mannlicher rifle, designed to function smoothly through the Schönauer's rotary magazine. 6.5 mm bullets are typically known for their high ballistic coefficients and sectional density, which gives them great stability in flight, resistance to wind deflection, and high penetrating power. It, along with the Mannlicher–Schönauer rifle, was first introduced in Paris at the 1900 World's Fair.
The 6.5×54mm Mannlicher–Schönauer cartridge was adopted by the Greek Army, along with the Mannlicher–Schönauer rifle in 1903. From 1906 until the German invasion and capitulation of Greece in April 1941, it was the standard military cartridge of the Greek Army. The Mannlicher-Carcano round was also used by Greek forces in this rifle, being with its cartridge just 2mm smaller than the desired bullet. During the German occupation it was used by Greek resistance fighters and during the Greek Civil War (1946 - 1949) by the Greek Gendarmerie, militia units and communist fighters of the Democratic Army of Greece. During the German occupation, Carcano rifles captured during World War II were also converted to 6.5×54mm Mannlicher–Schönauer and used by Greek forces.
The Austrian Army used the 6.5×54mm Mannlicher–Schönauer cartridge during World War I. Some Austrian Army regiments and the Polish Legion, were armed with confiscated Mannlicher–Schönauer rifles produced for the Greek Army. Also the Austrian Army used the 6.5×54 Mannlicher–Schönauer cartridge in converted 6.5×50mm Arisaka rifles captured from the Russian Army.