The Mauser, Oberndorf commercial serial number 10096 dates the action of that Steigleder rifle to 1905. The rifle was most likely completed within a year. According to “Der Waffenschmied” Mauser introduced their new 10.75x68 in 1909, some years later. Another year later, October 1910, the Rottweil powder factory renamed their experimental smokeless powder # 1550 to R5 and released it to the public. So a 1905 – 06 made rifle can not be meant to use the 10.75x68 nor R5 powder originally.
There are some more quirks with the two cartridges: When the Vienna gunmaker designed the 10.75x63, it was not meant for use on African thick skinned Big Game. As Austria had no colonies or interests on that continent, they saw little need for elephant or buffalo stoppers. Pre-WW1 Austria was not the small, alpine country we know today. Trieste (Italy), Prague (Czech), Krakau (Krakow in Poland), Pressburg (Bratislava in Slowakia), Lemberg (Lviv in Ukraine) and even Sarajevo were all Austro -Hungarian cities at that time. The realm of the K&K monarchy encompassed the most famous and wildest hunting grounds in all Europe. World’s largest red deer, in size approaching the American elk, brown bears (a cousin of the grizzly), huge wild boar and wolves still roam the dense forests of the Carpathian Mountains and the reed jungles of Slavonia. Hunting conditions are more similar to some of the north-western United States and what served Elmer Keith 25 years later also did the job for the hunters in those remote and unspeakable wildernesses. Elmer Keith´s beloved .400 Whelen was duplicated by the 10,75x63 and the 9x63 Florstedt occupied the place of the .35 Whelen. These were the conditions the 10.75x63 and x68 loads were meant for, not thick skinned African game.
Both cartridges were always loaded with 347 gr bullets only, but bullets of quite different designs. There were rn, flat nose ones with varying jacket lengths, hollow points and solids. And then there was an originally Austrian design called OE, an expanding full metal jacket with a large cavity below the jacket nose. As it looked like a solid, it was sometimes misused as such with disastrous results.
As Lancaster already noted, we found just one load for the 10.75x63 in an old Steigleder catalog: 3.8 gram = 58.6 gr R5 for 650 m/s = 2130 fps (barrel length unknown, likely 70 cm). But up to WW2 both RWS and DWM offered two loads for the 10.75x68: The full power load” for international use was 4.20 gram = 65 gr for 670 m/s = 2200 FPS (60 cm barrel) and a “mild load” for European brush use, 3.8 gram = 58.6 gr R5 for 610 m/s = 2000 fps (60 cm barrel). Incidentally, the same load as the earlier 10.75x63! Of course, mixing up these loads and bullet types without reading or understanding the package inscriptions will cause all sorts of mishap, from inaccuracy (not shooting to the sights) to unexpected bullet breakup.