I think this text helps to understand better greek Mannlicher´s history:

http://www.hungariae.com/Mann03.htm

"Related Greek Military History
From pages 555 & 556 of Christos Z. Sazanidis: The Arms of Hellenes, a Historical Survey of the Small Arms of the Hellenic Arms Forces, the Security Forces, and Guerilla Bands, (1821-1992)", Thessaloniki, Greece, 1995.
4. The Repeating Rifle Era (1905-1941) For Greece, the first decades of the 20th century was full of war events. The armed phase of the Macedonian Struggle (1904-1908), the victorious Balkan Wars (1912-1913), WW I (1914-1918), and the campaigns to Russia 1919) and Asia Minor (1919-1922) had all a decisive effect upon the organization and the armament of the Greek Armed Forces.
4a. Up to WW I (1905-1914) The armed phase of the Macadonian Struggle last 4 years (1094-1908) and Greece took active part in it by sending men and arms to this region. The small arms used by the Greek armed guerillas (andartae) who participated in the conflict were Gras and Martini single shot rifles and carbines.
After 1905, there was also a limited number of 6.5 mm Mannlicher-Schönauer repeating carbines, which were slightly different from those adopted by the Army. An assortment of rifles and carbines, coming from war booties (9.5mm and 7.65mm Turkish Mausers and 8x56mm Bulgarian Mannlichers) and commercial sales, was also used.
In the field of handguns, most were Chamelot-Delvigne and Montenegrin Gasser revolvers, but any other type of pistols and revolvers (Nagant, Colt, Smith & Wesson, Mannlicher etc) could also be seen in the hands of Greek guerillas. In Athens, after long debates and repeated trials, the Army adopted the 6.5mm Mannlicher-Schönauer repeating rifle and carbine on October 28, 1904. The first contract between Greece and the Steyr company (Oesterreichische Waffenfabrik Gesellschaft, Steyr) was signed on October 29-November 11, 1905 for 60,000 rifles and the first weapons were issued to troops in July, 1907. Up to the autumn of 1912, when the first Balkan War began, 130,000 Mannlicher-Schönauer rifles and carbines had been delivered to Greece, along with 100 million 6.5 mm cartridges bought from the Austrian Hirtenberger and Georg Roth companies, and the Greek Powder and Cartridge Company.
This rifle was used in both Balkan Wars, WW I, the campaigns to Russia and Asia Minor and the Greco-Italian and Greco-German Wars of 1940-41. It was also used by the resistance organizations during Axis occupation of Greece.
B. Up to the Treaty of Lausanne (1914-1923) When WW I broke out, Greece preferred to remain neutral for a certain period. This neutrality caused her to be cut off from any possible channel of armament procurement, including small arms and ammunition. Till then, Greece had in her arsenal 190,069 6.5mm M1903 and M1903/14 Mannlicher Schönauer rifles & carbines, 77,000 11mm M.1874 Gras rifles & carbines, and 44,000 Turkish Mausers and Bulgarian Mannlicher rifles and carbines.
C. Up to the Eve of the Greco-Italian War (1923 to October 27, 1940). After the Asia Minor debacle, the salvaged material, inter alia, included: 1. 96,000 6.5 mm M1903 and m1903/14 Mannlicher-Schönauer rifles 2. 8,650 M1903 Mannlicher-Schönauer carbines 3. 16,000 8 mm M1888/90 and m1895 Bulgarian Mannlicher rifles 4. 700 8 mm M1890 and m1895 Bulgarian Mannlicher carbines. 5. 26,000 7.65 mm M1890, M1893, and M1903 Turkish Mauser rifles 6. 10,500 7.65 mm M1890 and M1905 Turkish Mauser carbines. 7. 9,150 M1898 Mauser rifles8. etc.
All these weapons were old, worn out an short of spare parts, while most of them needed repair. In order (for) the Army to be ready for combat, new small arms had to be bought. After long debates and repeated trials, in 1925, Greece ordered tom the Italian Breda Factory 100,000 6.5 mm M1904/14/27 Mannlicher-Schönauer rifles, which were delivered in 1927. In 1930, Greece also purchased from Steyr Werke AG (SWAG), 25,000 6.5 mm M1904/14/30 Mannlicher Schoenauer carbines, making a total of 224,700 Mannlicher-Schönauer weapons (old and new)."

I personal think that greek Mannlicher special calibers have quite similar history alike finnish wildcats to x53R Mosin case.