This is what I found:

In 1917 Brenneke necked down his 8x64mm S design of 1912 to 7 mm calibre and introduced it as 7x64mm and achieved a major commercial success. The 7x64mm offered compared to the 7x57mm about 10 to 12 % extra muzzle velocity. This results in a flatter trajectory and better performance at longer range. In the years between World War I and World War II the 7x64mm was often regarded by German hunters as a “miracle cartridge” and dozens of different factory loads where available on the German market. It was that highly regarded the German Wehrmacht (Army) during the 1930s even considered replacing the 8x57mm IS in favour for the 7x64mm for their snipers. The Wehrmacht decided - just like the German army in 1912 - to stick to the 8x57mm IS cartridge for their Mauser Karabiner 98k to keep things as simple as possible in their logistical chain.